Hollow porous fibers

ABSTRACT

A hollow fiber that generally extends in a longitudinal direction is provided. The hollow fiber comprises a hollow cavity that extends along at least a portion of the fiber in the longitudinal direction. The cavity is defined by an interior wall that is formed from a thermoplastic composition containing a continuous phase that includes a polyolefin matrix polymer and a nanoinclusion additive dispersed within the continuous phase in the form of discrete domains. A porous network is defined in the composition that includes a plurality of nanopores.

RELATED APPLICATIONS

The present application is the national stage entry of InternationalPatent Application No. PCT/US2014/069705 having a filing date of Dec.11, 2014, which claims priority to International Application Serial No.PCT/IB2014/062022 filed on Jun. 6, 2014), which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

Fibrous materials are used in a wide variety of different component tohelp control the flow of fluids. In absorbent articles, for instance,fibrous materials (e.g., nonwoven webs) can be used to rapidly absorbbodily fluids (e.g., urine) and allow them to flow into an absorbentlayer without permitting or facilitating re-transmission of the fluidsto the wearer. Unfortunately, fibrous materials can experience multipleproblems when used in this manner. For example, it is often desirable tolower the basis weight of the fibrous material to allow for theformation of thinner products. With most conventional fibrous materials,however, such a reduction in basis weight can adversely impact otherproperties, such as liquid strikethrough and barrier properties. Whilesome solutions to these problems have been proposed, none are fullysatisfactory. For example, U.S. Pat. No. 6,368,990 describes a spunbondnonwoven web that is formed from hollow filaments or staple fibers.According to the '990 patent, such hollow fibers can allow for a lowerbasis weight or an increase in the number of fibers for a given basisweight. Nevertheless, despite achieving some improvement, these hollowstill suffer from multiple deficiencies. For example, the fibers tend tolack a sufficient degree of porosity to significantly improve the fluidintake properties of the material beyond what is already conventional.As such, a need currently exists for improve fibers and fibrousmaterials for use in a wide variety of different applications.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a hollowfiber that generally extends in a longitudinal direction is disclosed.The hollow fiber comprises a hollow cavity that extends in thelongitudinal direction along at least a portion of the fiber. The cavityis defined by an interior wall that is formed from a thermoplasticcomposition containing a continuous phase that includes a polyolefinmatrix polymer and a nanoinclusion additive dispersed within thecontinuous phase in the form of discrete domains. A porous network isdefined in the composition that includes a plurality of nanopores.

In accordance with another embodiment of the present invention, a methodfor forming a hollow fiber is disclosed that comprises forming athermoplastic composition that contains a continuous phase that includesa polyolefin matrix polymer and a nanoinclusion additive dispersedwithin the continuous phase in the form of discrete domains; extrudingthe composition through a capillary to form the fiber, wherein one ormore shaped slots are positioned within the capillary; and drawing thefiber at a temperature that is lower than the melting temperature of thematrix polymer, thereby forming a porous network that includes aplurality of nanopores.

Other features and aspects of the present invention are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification, whichmakes reference to the appended figures in which:

FIG. 1 is a perspective view of one embodiment of the absorbent articlethat may employ the hollow fibers of the present invention;

FIG. 2 is a schematic illustration of a process that may be used in oneembodiment of the present invention to form hollow fibers;

FIG. 3 is a bottom view of one embodiment of a spinneret that may beemployed to form the hollow fibers of the present invention;

FIG. 4 is a cross-sectional view of the spinneret of FIG. 3 taken alonga line 4-4;

FIGS. 5-6 are SEM photomicrographs of the fiber of Example 1 afterfreeze fracturing in liquid nitrogen; and

FIGS. 7-8 are SEM photomicrographs of the fiber of Example 2 afterfreeze fracturing in liquid nitrogen.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

Reference now will be made in detail to various embodiments of theinvention, one or more examples of which are set forth below. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and vacations may be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, may be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Generally speaking, the present invention is directed to a hollow fiberthat contains a hollow cavity extending along at least a portion of thefiber along a longitudinal axis thereof. The cavity is defined by aninterior wall, which is itself porous in nature. More particularly, thewall is at least partially formed by a thermoplastic composition thatcontains a continuous phase, which includes a polyolefin matrix polymer,and a nanoinclusion additive that is at least partially incompatiblewith the polyolefin matrix polymer so that it becomes dispersed withinthe continuous phase as discrete nano-scale phase domains. Duringdrawing of the fiber, the present inventors have discovered that thesenano-scale phase domains are able to interact in a unique manner tocreate a network of pores in the interior wall of the fiber. Namely, itis believed that elongational strain experienced during drawing caninitiate intensive localized shear zones and/or stress intensify zones(e.g., normal stresses) near the discrete phase domains as a result ofstress concentrations that arise from the incompatibility of thematerials. These shear and/or stress intensity zones cause some initialdebonding in the polyolefin matrix adjacent to the domains. Once initialpores are formed, the matrix located between domains can deformplastically to create internal stretched areas that locally narrow (orneck) and strain-harden. This process allows the formation of poresthrough the bulk of the interior wall that grow in the stretchingdirection, thereby leading to the formation of a porous network whilethe molecular orientation leads to strain-hardening that enhancesmechanical strength.

Notably, a substantial portion of these pores may be of a “nano-scale”size (“nanopores”), such as those having an average cross-sectionaldimension of about 800 nanometers or less, in some embodiments fromabout 5 to about 700 nanometers, and in some embodiments, from about 10to about 500 nanometers. The term “cross-sectional dimension” generallyrefers to a characteristic dimension (e.g., width or diameter) of apore, which is substantially orthogonal to its major axis (e.g., length)and also typically substantially orthogonal to the direction of thestress applied during drawing. The nanopores may also have an averageaxial dimension within the range of from about 100 to about 5000nanometers, in some embodiments from about 50 to about 2000 nanometers,and in some embodiments, from about 100 to about 1000 nanometers. The“axial dimension” is the dimension in the direction of the major axis(e.g., length), which is typically in the direction of drawing.

As will be described in more detail below, the interior wall can beformed from a single polymer layer (e.g., a monocomponent fiber) ormultiple polymer layers (e.g., a bicomponent fiber). Regardless, therelative size of the porous interior wall may also be selectivelycontrolled in the present invention to achieve a hollow fiber with thedesired properties. For instance, the interior wall may have an averagewall thickness of from about 0.5 to about 50 micrometers, in someembodiments from about 1 to about 30 micrometers, and in someembodiments, from about 2 to about 15 micrometers. To enhance theproperties of the fiber, the inner diameter of the wall (e.g., diameterof the cavity) is typically controlled so that it is greater than theinterior wall thickness. The ratio of the average inner diameter to theaverage wall thickness may, for instance, range from about 1:1 to about40:1, preferably from about 1.5:1 to about 30:1, and some embodiments,from about 2:1 to about 20:1. The average inner diameter of the wallmay, for instance, range from about 1 to about 100 micrometers, in someembodiments from about 2 to about 60 micrometers, and in someembodiments, from about 4 to about 30 micrometers. The average outerdiameter of the wall, which may or may not be the same as the overallfiber diameter, may likewise range from about 2 to about 200micrometers, in some embodiments from about 5 to about 100 micrometers,and in some embodiments, from about 10 to about 50 micrometers. Itshould be understood that the actual wall thickness and diameter valuesmay vary somewhat along the longitudinal axis of the fiber.Nevertheless, one benefit of the present invention is that such valuesmay remain relatively constant such that the coefficient of variation inwall thickness, inner diameter, and/or outer diameter of about 20% orless, in some embodiments about 15% or less, and in some embodiments,about 10% or less along the longitudinal direction of the fiber.

Through the techniques noted above, the resulting hollow fiber may havean average percent pore volume within a given unit volume of the fiberof from about 25% to about 80% per cm³, in some embodiments from about30% to about 75%, and in some embodiments, from about 40% to about 70%per cubic centimeter of the fiber. The nanopores may, for example,constitute about 15 vol. % or more, in some embodiments about 20 vol. %or more, in some embodiments from about 30 vol. % to 100 vol. %, and insome embodiments, from about 40 vol. % to about 90 vol. % of the totalpore volume in the polyolefin fiber. With such a pore volume, thecomposition may have a relatively low density, such as about 0.90 gramsper cubic centimeter (“g/cm³”) or less, in some embodiments about 0.85g/cm³ or less, in some embodiments about 0.08 g/cm³ or less, in someembodiments from about 0.10 g/cm³ to about 0.75 g/cm³, and in someembodiments, from about 0.20 g/cm³ to about 0.70 g/cm³.

Various embodiments of the present invention will now be described inmore detail.

I. Thermoplastic Composition

A. Polyolefin Matrix

Polyolefins typically constitute from about 60 wt. % to about 99 wt. %,in some embodiments from about 60 wt. % to about 98 wt. %, and in someembodiments, from about 80 wt. % to about 95 wt. % of the thermoplasticcomposition. The polyolefin may have a melting temperature of from about100° C. to about 220° C., in some embodiments from about 120° C. toabout 200° C., and in some embodiments, from about 140° C. to about 180°C. The melting temperature may be determined using differential scanningcalorimetry (“DSC”) in accordance with ASTM D-3417. Suitable polyolefinsmay, for instance, include ethylene polymers (e.g., low densitypolyethylene (“LDPE”), high density polyethylene (“HDPE”), linear lowdensity polyethylene (“LLDPE”), etc.), propylene homopolymers (e.g.,syndiotactic, atactic, isotactic, etc.), propylene copolymers, and soforth. In one particular embodiment, the polymer is a propylene polymer,such as homopolypropylene or a copolymer of propylene. The propylenepolymer may, for instance, be formed from a substantially isotacticpolypropylene homopolymer or a copolymer containing equal to or lessthan about 10 wt. % of other monomers, i.e., at least about 90% byweight propylene. Such homopolymers may have a melting point of fromabout 140° C. to about 170° C.

Of course, other polyolefins may also be employed in the composition ofthe present invention. In one embodiment, for example, the polyolefinmay be a copolymer of ethylene or propylene with another α-olefin, suchas a C₃-C₂₀ α-olefin or C₃-C₁₂ α-olefin. Specific examples of suitableα-olefins include 1-butene; 3-methyl-1-butene; 3,3-dimethyl-1-butene;1-pentene; 1-pentene with one or more methyl, ethyl or propylsubstituents; 1-hexene with one or more methyl, ethyl or propylsubstituents; 1-heptene with one or more methyl, ethyl or propylsubstituents; 1-octene with one or more methyl, ethyl or propylsubstituents; 1-nonene with one or more methyl, ethyl or propylsubstituents; ethyl, methyl or dimethyl-substituted 1-decene;1-dodecene; and styrene. Particularly desired α-olefin comonomers are1-butene, 1-hexene and 1-octene. The ethylene or propylene content ofsuch copolymers may be from about 60 mole % to about 99 mole %, in someembodiments from about 80 mole % to about 98.5 mole %, and in someembodiments, from about 87 mole % to about 97.5 mole %. The α-olefincontent may likewise range from about 1 mole % to about 40 mole %, insome embodiments from about 1.5 mole % to about 15 mole %, and in someembodiments, from about 2.5 mole % to about 13 mole %.

Exemplary olefin copolymers for use in the present invention includeethylene-based copolymers available under the designation EXACT™ fromExxonMobil Chemical Company of Houston, Tex. Other suitable ethylenecopolymers are available under the designation ENGAGE™, AFFINITY™,DOWLEX™ (LLDPE) and ATTANE™ (ULDPE) from Dow Chemical Company ofMidland, Mich. Other suitable ethylene polymers are described in U.S.Pat. No. 4,937,299 to Ewen et al.; U.S. Pat. No. 5,218,071 to Tsutsui etal.; U.S. Pat. No. 5,272,236 to Lai, et al.; and U.S. Pat. No. 5,278,272to Lai, et al. Suitable propylene copolymers are also commerciallyavailable under the designations VISTAMAXX™ from ExxonMobil Chemical Co.of Houston, Tex.; FINA™ (e.g., 8573) from Atofina Chemicals of Feluy,Belgium; TAFMER™ available from Milsui Petrochemical Industries; andVERSIFY™ available from Dow Chemical Co. of Midland, Mich. Suitablepolypropylene homopolymers may include Exxon Mobil 3155 polypropylene,Exxon Mobil Achiev™ resins, and Total M3661 PP resin. Other examples ofsuitable propylene polymers are described in U.S. Pat. No. 6,500,563 toDatta, et al.; U.S. Pat. No. 5,539,056 to Yang, et al.; and U.S. Pat.No. 5,596,052 to Resconi, et al.

Any of a variety of known techniques may generally be employed to formthe olefin copolymers. For instance, olefin polymers may be formed usinga free radical or a coordination catalyst (e.g., Ziegler-Natta).Preferably, the olefin polymer is formed from a single-site coordinationcatalyst, such as a metallocene catalyst. Such a catalyst systemproduces ethylene copolymers in which the comonomer is randomlydistributed within a molecular chain and uniformly distributed acrossthe different molecular weight fractions. Metallocene-catalyzedpolyolefins are described, for instance, in U.S. Pat. No. 5,571,619 toMcAlpin et al.; U.S. Pat. No. 5,322,728 to Davis et al.; U.S. Pat. No.5,472,775 to Obijeski et al.; U.S. Pat. No. 5,272,236 to Lai et al.; andU.S. Pat. No. 6,090,325 to Wheat, et al. Examples of metallocenecatalysts include bis(n-butylcyclopentadienyl)titanium dichloride,bis(n-butylcyclopentadienyl)zirconium dichloride,bis(cyclopentadienyl)scandium chloride, bis(indenyl)zirconiumdichloride, bis(methylcyclopentadienyl)titanium dichloride,bis(methylcyclopentadienyl)zirconium dichloride, cobaltocene,cyclopentadienyltitanium trichloride, ferrocene, hafnocene dichloride,isopropyl(cyclopentadienyl,-1-flourenyl)zirconium dichloride,molybdocene dichloride, nickelocene, niobocene dichloride, ruthenocene,titanocene dichloride, zirconocene chloride hydride, zirconocenedichloride, and so forth. Polymers made using metallocene catalyststypically have a narrow molecular weight range. For instance,metallocene-catalyzed polymers may have polydispersity numbers(M_(w)/M_(n)) of below 4, controlled short chain branching distribution,and controlled isotacticity.

B. Nanoinclusion Additive

As used herein, the term “nanoinclusion additive” generally refers to amaterial that is capable of being dispersed within the polymer matrix inthe form of discrete domains of a nano-scale size. For example, prior todrawing, the domains may have an average cross-sectional dimension offrom about 1 to about 1000 nanometers, in some embodiments from about 5to about 800 nanometers, in some embodiments from about 10 to about 500nanometers, and in some embodiments from about 20 to about 200nanometers. The domains may have a variety of different shapes, such aselliptical, spherical, cylindrical, plate-like, tubular, etc. In oneembodiment, for example, the domains have a substantially ellipticalshape. The nanoinclusion additive is typically employed in an amount offrom about 0.05 wt. % to about 20 wt. %, in some embodiments from about0.1 wt. % to about 10 wt. %, and in some embodiments, from about 0.5 wt.% to about 5 wt. % of the thermoplastic composition, based on the weightof the continuous phase polyolefin matrix. The concentration of thenanoinclusion additive in the entire thermoplastic composition maylikewise be from about 0.01 wt. % to about 15 wt. %, in some embodimentsfrom about 0.05 wt. % to about 10 wt. %, and in some embodiments, fromabout 0.3 wt. % to about 6 wt. % of the thermoplastic composition.

The nanoinclusion additive is partially incompatible with the polyolefinin the sense that it can be substantially uniformly distributed withinthe polyolefin matrix, but in the form of discrete domains. Such partialincompatibility can be accomplished in a variety of ways. In certainembodiments, for example, the nanoinclusion additive may possess anonpolar component (e.g., olefin) that is compatible with the polyolefinmatrix and allows it to become uniformly distributed therein.Nevertheless, the additive may also include a polar component that isincompatible with the polyolefin matrix, thereby allowing it to coalesceor segregate into discrete domains. Such a component may include low orhigh molecular weight polar molecular segments or blocks, ionic groups,charged or uncharged polar domains, and/or polar molecular groups.Alternatively, the additive may be entirely nonpolar in nature, butpossess certain physical properties that still allow for discretedomains to be formed. For example, in certain embodiments, thenanoinclusion additive may be compatible or miscible with the polyolefinabove a certain temperature, but phase separate at temperatures lowerthan the critical solution temperature. In this manner, thenanoinclusion additive can form a stable blend with the polyolefin inthe melt phase, but as the temperature decreases, the continuous phasecrystallizes and segregates so that the nanoinclusion additive can phaseseparate, coalesce, and form separate nano-scale domains.

The particular state or form of the nanoinclusion additive is notcritical so long as the desired domains can be formed. For example, insome embodiments, the nanoinclusion additive can be in the form of aliquid or semi-solid at room temperature (e.g., 25° C.). Such a liquidcan be readily dispersed in the matrix to form a metastable dispersion,and then quenched to preserve the domain size by reducing thetemperature of the blend. The kinematic viscosity of such a liquid orsemi-solid material is typically from about 0.7 to about 200 centistokes(“cs”), in some embodiments from about 1 to about 100 cs, and in someembodiments, from about 1.5 to about 80 cs, determined at 40° C.Suitable liquids or semi-solids may include, for instance, silicones,silicone-polyether copolymers, aliphatic polyesters, aromaticpolyesters, alkylene glycols (e.g., ethylene glycol, diethylene glycol,triethylene glycol, tetraethylene glycol, propylene glycol, polyethyleneglycol, polypropylene glycol, polybutylene glycol, etc.), alkane diols(e.g., 1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,6hexanediol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol,2,2,4,4-tetramethyl-1,3-cyclobulanediol, etc.), amine oxides (e.g.,octyldimethylamine oxide), fatty acid esters, fatty acid amides (e.g.,oleamide, erucamide, stearamide, ethylene bis(stearamide), etc.),mineral, and vegetable oils, and so forth. One particularly suitableliquid or semi-solid is polyether polyol, such as commercially availableunder the trade name Pluriol® WI from BASF Corp.

In yet other embodiments, the nanoinclusion additive is in the form of asolid, which may be amorphous, crystalline, or semi-crystalline. Forexample, the nanoinclusion additive may be polymeric in nature andpossess a relatively high molecular weight to help improve the meltstrength and stability of the thermoplastic composition. As indicatedabove, the nanoinclusion additive is partially incompatible with thepolyolefin matrix. One example of such an additive is a microcrystallinepolyolefin wax, which is typically derived torn ethylene and/orC₃-C₁₀-alk-1-enes, such as from propylene, 1-butene, 1-pentene,1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene. Microcrystaliinewaxes typically have a relatively low mating temperature, such as fromabout 30° C. to about 150° C., in some embodiments from about 50° C. toabout 140° C., and in some embodiments, from about 80° C. to about 130°C. At such low melting temperatures, the wax can form a miscible blendwith the polyolefin when in the melt phase, but as the temperaturedecreases and polymer crystalizes or solidifies, the wax will segregateand coalesce forming separate nano-scale domains.

Another example of a polymeric nanoinclusion additive is afunctionalized polyolefins that contains a polar and nonpolar component.The polar component may, for example, be provided by one or morefunctional groups and the nonpolar component may be provided by anolefin. The olefin component of the nanoinclusion additive may generallybe formed from any linear or branched α-olefin monomer, oligomer, orpolymer (including copolymers) derived from an olefin monomer, such asdescribed above. The functional group of the nanoinclusion additive maybe any group, molecular segment and/or block that provides a polarcomponent to the molecule and is not compatible with the polyolefinmatrix polymer. Examples of molecular segment and/or blocks notcompatible with polyolefin may include acrylates, styrenics, polyesters,polyamides, etc. The functional group can have an ionic nature andcomprise charged metal ions. Particularly suitable functional groups aremaleic anhydride, maleic acid, fumaric acid, maleimide, maleic acidhydrazide, a reaction product of maleic anhydride and diamine,methylnadic anhydride, dichloromaleic anhydride, maleic acid amide, etc.Maleic anhydride modified polyolefins are particularly suitable for usein the present invention. Such modified polyolefins are typically formedby grafting maleic anhydride onto a polymeric backbone material. Suchmaleated polyolefins are available from E. I. du Pont de Nemours andCompany under the designation Fusabond®, such as the P Series(chemically modified polypropylene), E Series (chemically modifiedpolyethylene), C Series (chemically modified ethylene vinyl acetate), ASeries (chemically modified ethylene acrylate copolymers orterpolymers), or N Series (chemically modified ethylene-propylene,ethylene-propylene diene monomer (“EPDM”) or ethylene-octene).Alternatively, maleated polyolefins are also available from ChemturaCorp. under the designation Polybond®, Eastman Chemical Company underthe designation Eastman G series, and Arkema under the designationOrevac®.

In certain embodiments, the polymeric nanoinclusion additive may also bereactive. One example of such a reactive nanoinclusion additive is apolyepoxide that contains, on average, at least two oxirane rings permolecule. Without intending to be limited by theory, it is believed thatsuch polyepoxide molecules can undergo a reaction (e.g., chainextension, side chain branching, grafting, copolymer formation, etc.)with certain components of the composition to improve melt strengthwithout significantly reducing glass transition temperature. Thereactive additive can also provide compatibilization between thepolyolefin and other more polar additives, such as microinclusionadditives, and can improve the uniformity of dispersion and reduce thesize of microinclusion additives. For example, as will be described inmore detail below, certain embodiments of the present invention mayemploy a polyester as a microinclusion additive. In such embodiments,the reactive nanoinclusion additive may enable a nucleophilicring-opening reaction via a carboxyl terminal group of the polyester(esterification) or via a hydroxyl group (etherification). Oxazolineside reactions may likewise occur to form esteramide moieties. Throughsuch reactions, the molecular weight of a polyester microinclusionadditive may be increased to counteract the degradation often observedduring melt processing. The present inventors have discovered that toomuch of a reaction can lead to crosslinking between polymer backbones.If such crosslinking is allowed to proceed to a significant extent, theresulting polymer blend can become brittle and difficult to process intoa fiber with the desired strength and elongation properties.

In this regard, the present inventors have discovered that polyepoxideshaving a relatively low epoxy functionality may be particularlyeffective, which may be quantified by its “epoxy equivalent weight.” Theepoxy equivalent weight reflects the amount of resin that contains onemolecule of an epoxy group, and it may be calculated by dividing thenumber average molecular weight of the modifier by the number of epoxygroups in the molecule. The polyepoxide of the present inventiontypically has a number average molecular weight from about 7,500 toabout 250,000 grams per mole, in some embodiments from about 15,000 toabout 150,000 grams per mole, and in some embodiments, from about 20,000to 100,000 grams per mole, with a polydispersity index typically rangingfrom 2.5 to 7. The polyepoxide may contain less than 50, in someembodiments from 5 to 45, and in some embodiments, from 15 to 40 epoxygroups. In turn, the epoxy equivalent weight may be less than about15,000 grams per mole, in some embodiments from about 200 to about10,000 grams per mole, and in some embodiments, from about 500 to about7,000 grams per mole.

The polyepoxide may be a linear or branched, homopolymer or copolymer(e.g., random, graft, block, etc.) containing terminal epoxy groups,skeletal oxirane units, and/or pendent epoxy groups. The monomersemployed to form such polyepoxides may vary. In one particularembodiment, for example, the polyepoxide contains at least oneepoxy-functional (meth)acrylic monomeric component. As used herein, theterm “(meth)acrylic” includes acrylic and methacrylic monomers, as wellas salts or esters thereof, such as acrylate and methacrylate monomers.For example, suitable epoxy-functional (meth)acrylic monomers mayinclude, but are not limited to, those containing 1,2-epoxy groups, suchas glycidyl acrylate and glycidyl methacrylate. Other suitableepoxy-fonctional monomers include allyl glyclciyl ether, glycidylethacrylate, and glycidyl itoconate.

The polyepoxide typically has a relatively high molecular weight, asindicated above, so that it may not only result in chain extension, butalso help to achieve the desired blend morphology. The resulting meltflow rate of the polymer is thus typically within a range of from about10 to about 200 grams per 10 minutes, in some embodiments from about 40to about 150 grams per 10 minutes, and in some embodiments, from about60 to about 120 grams per 10 minutes, determined at a load of 2160 gramsand at a temperature of 190° C.

The polyepoxide also typically induces at least one linear or branchedα-olefin monomer, such as those having from 2 to 20 carbon atoms andpreferably from 2 to 8 carbon atoms. Specific examples include ethylene,propylene, 1-butene; 3-methyl-1-butene; 3,3-dimethyl-1-butane;1-pentene; 1-pentane with one or more methyl, ethyl or propylsubstituents; 1-hexene with one or more methyl, ethyl or propylsubstituents; 1-heptane with one or more methyl, ethyl or propylsubstituents; 1-octene with one or more methyl, ethyl or propylsubstituents; 1-nonene with one or more methyl, ethyl or propylsubstituents, ethyl, methyl or dimethyl-substitued 1-decene; 1-dodecene;and styrene. Particularly desired α-olefin comonomers are ethylene andpropylene. Another suitable monomer may include a (meth)acrylic monomerthat is not epoxy-functional. Examples of such (meth)acrylic monomersmay include methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propylacrylafe, n-butyl acrylate, s-butyl acrylate, i-butyl acrylate, t-butylacrylate, n-amyl acrylate, i-amyl acrylate, isobornyl acrylate, n-hexylacrylate, 2-ethylbutyl acrylate, 2-ethylhexyl acrylate, n-octylacrylate, n-decyl acrylate, methylcyclohexyl acrylate, cyclopentylacrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate,2-hydroxyethyl methacrylate, n-propyl methacrylate, n-butylmelhacrylate, i-propyl methacrylate, i-butyl methacrylate, n-amylmethacrylate, n-hexyl methacrylate, i-amyl methacrylate,s-butyl-methacrylate, t-butyl methacrylate, 2-ethylbutyl methacrylate,methyloyolohexyl methacrylate, cinnamyl methacrylate, crotylmetbacrylate, cyclohexyl methacrylate, cyclopentyl methacrylate,2-ethoxyethyl methacrylate, isobornyl methacrylate, etc., as well ascombinations thereof.

In one particularly desirable embodiment of the present invention, thepolyepoxide is a terpolymer formed from an epoxy-functional(meth)acrylic monomeric component, α-olefin monomeric component, andnon-epoxy functional (meth)acrylic monomeric component. For example, thepolyepoxide may be poly(ethylene-co-methylacryate-co-glycidylmethacrylate), which has the following structure:

wherein, x, y, and z are 1 or greater.

The epoxy functional monomer may be formed into a polymer using avariety of known techniques. For example, a monomer containing polarfunctional groups may be grated onto a polymer backbone to form a graftcopolymer. Such grafting techniques are well known in the art anddescribed, for instance, in U.S. Pat. No. 5,179,164. In otherembodiments, a monomer containing epoxy functional groups may becopolymerized with a monomer to form a block or random copolymer usingknown free radical polymerization techniques, such as high pressurereactions, Ziegler-Natta catalyst reaction systems, single site catalyst(e.g., metallocene) reaction systems, etc.

The relative portion of the monomeric component(s) may be selected toachieve a balance between epoxy-reactivity and melt flow rate. Moreparticularly, high epoxy monomer contents can result in good reactivity,but too high of a content may reduce the melt flow rate to such anextent that the polyepoxide adversely impacts the melt strength of thepolymer blend. Thus, in most embodiments, the epoxy-functional(meth)acryllc monomer(s) constitute from about 1 wt. % to about 25 wt.%, in some embodiments from about 2 wt. % to about 20 wt. %, and in someembodiments, from about 4 wt. % to about 15 wt. % of the copolymer. Theα-olefin monomer(s) may likewise constitute from about 55 wt. % to about95 wt. %, in some embodiments from about 60 wt. % to about 90 wt. %, andin some embodiments, from about 65 wt. % to about 85 wt. % of thecopolymer. When employed, other monomeric components (e.g., non-epoxyfunctional (meth)acrylic monomers) may constitute from about 5 wt. % toabout 35 wt. %, in some embodiments from about 8 wt. % to about 30 wt.%, and in some embodiments, from about 10 wt. % to about 25 wt. % of thecopolymer. One specific example of a suitable polyepoxide that may beused in the present invention is commercially available from Arkemaunder the name LOTADER® AX8950 or AX8900. LOTADER® AX8950, for instance,has a melt flow rate of 70 to 100 g/10 min and has a glycidylmethacrylate monomer content of 7 wt. % to 11 wt. %, a methyl acrylatemonomer content of 13 wt. % to 17 wt. %, and an ethylene monomer contentof 72 wt. % to 80 wt. %. Another suitable polyepoxide is commerciallyavailable from DuPont under the name ELVALOY® PTW, which is a terpolymerof ethylene, butyl acrylate, and glycidyl methacrylate and has a meltflow rate of 12 g/10 min.

In addition to controlling the type and relative content of the monomersused to form the polyepoxide, the overall weight percentage may also becontrolled to achieve the desired benefits. For example, if themodification level is too low, the desired increase in melt strength andmechanical properties may not be achieved. The present inventors havealso discovered, however, that if the modification level is too high,processing may be restricted due to strong molecular interactions (e.g.,crosslinking) and physical network formation by the epoxy functionalgroups. Thus, the polyepoxide is typically employed in an amount of fromabout 0.05 wt. % to about 10 wt. %, in some embodiments from about 0.1wt. % to about 8 wt. %, in some embodiments from about 0.5 wt. % toabout 5 wt. %, and in some embodiments, from about 1 wt. % to about 3wt. %, based on the weight of the polyolefins employed in thecomposition. The polyepoxide may also constitute from about 0.05 wt. %to about 10 wt. %, in some embodiments from about 0.05 wt. % to about 8wt. %, in some embodiments from about 0.1 wt. % to about 5 wt. %, and insome embodiments, from about 0.5 wt. % to about 3 wt. %, based on thetotal weight of the composition.

Other reactive nanoinclusion additives may also be employed in thepresent invention, such as oxazoline-functionalized polymers,cyanide-functionalized polymers, etc. When employed, such reactivenanoinclusion additives may be employed within the concentrations notedabove for the polyepoxide. In one particular embodiment, anoxazoline-grafted polyolefin may be employed that is a polyolefingrafted with an oxazoline ring-containing monomer. The oxazoline mayinclude a 2-oxazoline, such as 2-vinyl-2-oxazoline (e.g.,2-isopropenyl-2-oxazoline), 2-fatty-alkyl-2-oxazolinene (e.g.,obtainable from the ethanolamide of oleic acid, linoleic acid,palmitoleic acid, gadoleic acid, erucic acid and/or arachidonic acid)and combinations thereof. In another embodiment, the oxazoline may beselected from ricinoloxazoline maleinate, undecyl-2-oxazoline,soya-2-oxazoline, ricinus-2-oxazoline and combinations thereof, forexample. In yet another embodiment, the oxazoline is selected from2-isopropenyl-2-oxazoline, 2-isopropenyl-4,4-dimethyl-2-oxazoline andcombinations thereof.

In certain embodiments of the present invention, multiple nanoinclusionadditives may be employed in combination. For instance, a firstnanoinclusion additive (e g., polyepoxide) may be dispersed in the formof domains having an average cross-sectional dimension of from about 50to about 500 nanometers, in some embodiments from about 60 to about 400nanometers, and in some embodiments from about 80 to about 300nanometers. A second nanoinclusion additive may also be dispersed in theform of domains that are smaller than the first nanoinclusive additive,such as those having an average cross-sectional dimension of from about1 to about 50 nanometers, in some embodiments from about 2 to about 45nanometers, and in some embodiments from about 5 to about 40 nanometers.When employed, the first and/or second nanoinclusion additives typicallyconstitute from about 0.05 wt. % to about 20 wt. %, in some embodimentsfrom about 0.1 wt. % to about 10 wt. %, and in some embodiments, fromabout 0.5 wt. % to about 5 wt. % of the thermoplastic composition, basedon the weight of the continuous phase (matrix polymer(s)). Theconcentration of the first and/or second nanonclusion additives in theentire thermoplastic composition may likewise be from about 0.01 wt. %to about 15 wt. %, in some embodiments from about 0.05 wt. % to about 10wt. %, and in some embodiments, from about 0.1 wt. % to about 8 wt. % ofthe thermoplastic composition.

Nanofillers may optionally be employed for the second nanoinclusionadditive, examples of which may induce carbon black, carbon nanotubes,carbon nanofibers, nanoclays, metal nanoparticles, nanosilica,nanoalumina, etc. Nanoclays are particularly suitable. The term“nanoclay” generally refers to nanoparticles of a clay material (anaturally occurring mineral, an organically modified mineral, or asynthetic nanomatenal), which typically have a platelet structure.Examples of nanoclays include, for instance, montmorillonite (2.1layered smectite clay structure), bentonite (aluminium phyllosilicateformed primarily of montmorillonite), kaolinite (1:1 aluminosilicatehaving a platy structure and empirical formula of Al₂Si₂O₅(OH)₄),halloysite (1:1 aluminosilicate having a tubular structure and empiricalformula of Al₂Si₂O₅(OH)₄), etc. An example of a suitable nanoclay isCloisite®, which is a montmorillonite nanoclay and commerciallyavailable from Southern Clay Products, Inc. Other examples of synthethicnanoclays include but are not limited to a mixed-metal hydroxidenanoclay, layered double hydroxide nanoclay (e.g., sepiocite), laponite,hectorite, saponite, indonite, etc.

If desired, the nanoclay may contain a surface treatment to help improvecompatibility with the marrix polymer (e.g., polyester). The surfacetreatment may be organic or inorganic. In one embodiment, an organicsurface treatment is employed that is obtained by reacting an organiccation with the clay. Suitable organic cations may include, forinstance, organoquaternary ammonium compounds that are capable ofexchanging cations with the clay, such as dimethyl bis[hydrogenatedtallow] ammonium chloride (2M2HT), methyl benzyl bis[hydrogenatedtallow] ammonium chloride (MB2HT), methyl tris[hydrogenated tallowalkyl] chloride (M3HT), etc. Examples of commercially available organicnanoclays may include, for instance, Dellite® 43B (Laviosa Chimica ofLivorno, Italy), which is a montmorillonite clay modified with dimethylbenzylhydrogenated tallow ammonium salt. Other examples includeCloisite® 25A and Cloisite® 30B (Southern Clay Products) and Nanofil 919(Süd Chemie). If desired, the nanofiller can be blended with a carrierresin to form a masterbatch that enhances the compatibility of theadditive with the other polymers in the composition. Particularlysuitable carrier resins include, for instance, polyesters (e.g.,polylactic acid, polyethylene terephthalate, etc,); polyolefins (e.g.,ethylene polymers, propylene polymers, etc.); and so forth, as describedin more detail above.

Regardless of the material employed, the nanoinclusion additive istypically selected to have a certain viscosity (or melt flow rate) toensure that the discrete domains and resulting pores can be adequatelymaintained. For example, if the viscosity of the nanoinclusion additiveis too low (or melt flow rate is too high), if tends to flow anddisperse uncontrollably through the continuous phase. This results inlamellar, plate-like domains or co-continuous phase structures that aredifficult to maintain and also likely to prematurely fracture.Conversely, if the viscosity is too high (or melt low rate is too low),it tends to clump together and form very large elliptical domains, whichare difficult to disperse during blending. This may cause unevendistribution of the nanoinclusion additive through the entirety of thecontinuous phase. For instance, the ratio of the melt flow rate of thepolyolefin to the melt flow rate of a polymeric nanoinclusion additive,for instance, may be from about 0.2 to about 8, in some embodiments fromabout 0.5 to about 6, and in some embodiments, from about 1 to about 5.The nanoinclusion additive may, for example, have a melt flow rate (on adry basis) of from about 0.1 to about 100 grams per 10 minutes, in someembodiments from about 0.5 to about 50 grams per 10 minutes, and in someembodiments, from a bout 5 to about 15 grams per 10 minutes, determinedat a load of 2160 grams and at a temperature at least about 4° C. abovethe melting temperature (e.g., at 190° C.) in accordance with ASTMD1238. The polyolefin may likewise have a melt flow rate (on a drybasis) of from about 0.5 to about 80 grams per 10 minutes, in someembodiments from about 1 to about 40 grams per 10 minutes, and in someembodiments, from about 5 to about 20 grams per 10 minutes, determinedat a load of 2160 grams and at a temperature at least about 40° C. abovethe melting temperature (e.g., at 230° C.) in accordance with ASTMD1238.

C. Microinclusion Additive

Although not required, the composition of the present invention may alsoemploy a microinclusion additive. As used herein, the term“microinclusion additive” generally refers to any material that iscapable of being dispersed within the polymer matrix in the form ofdiscrete domains of a micro-scale size. For example, prior to drawing,the domains may have an average cross-sectional dimension of from about0.1 μm to about 25 μm, in some embodiments from about 0.5 μm to about 20μm, and in some embodiments from about 1 μm to about 10 μm. Whenemployed, the present inventors have discovered that the micro-scale andnano-scale phase domains are able to interact in a unique manner whensubjected to a deformation and elongational strain (e.g., drawing) tocreate a network of pores. Namely, it is believed that elongationalstrain can initiate intensive localized shear zones and/or stressintensity zones (e.g., normal stresses) near the micro-scale discretephase domains as a result of stress concentrations that arise from theincompatibility of the materials. These shear and/or stress intensityzones cause some initial debonding in the polyolefin matrix adjacent tothe micro-scale domains. Notably, however, the localized shear and/orstress intensity zones created near the nano-scale discrete phasedomains may overlap with the micro-scale zones to cause even furtherdebonding to occur in the polymer matrix, thereby creating a substantialnumber of nanopores adjacent to the nano-scale domains and/ormicro-scale domains.

The particular nature of the microinclusion additive is not critical,and may include liquids, semi-solids, or solids (e.g., amorphous,crystalline, or semi-crystalline). In certain embodiments, themicroinclusion additive is polymeric in nature and possesses arelatively high molecular weight to help improve the melt strength andstability of the thermoplastic composition. Typically, themicroinclusion additive polymer may be generally incompatible with thematrix polymer. In this manner, the additive can better become dispersedas discrete phase domains within a continuous phase of the matrixpolymer. The discrete domains are capable of absorbing energy thatarises from an external force, which increases the overall toughness andstrength of the resulting fiber. The domains may have a variety ofdifferent shapes, such as elliptical, spherical, cylindrical,plate-like, tubular, etc. In one embodiment, for example, the domainshave a substantially elliptical shape. The physical dimension of anindividual domain is typically small enough to minimize the propagationof cracks through the fiber upon the application of an external stress,but large enough to initiate microscopic plastic deformation and allowfor shear zones at and around particle inclusions.

The microinclusion additive may have a certain melt flow rate (orviscosity) to ensure that the discrete domains and resulting pores canbe adequately maintained. For example, if the melt flow rate of theadditive is too high, it tends to flow and disperse uncontrollablythrough the continuous phase. This results in lamellar, plate-likedomains or co-continuous phase structures that are difficult to maintainand also likely to prematurely fracture. Conversely, if the melt flowrate of the additive is too low, it tends to clump together and termvery large elliptical domains, which are difficult to disperse duringblending. This may cause uneven distribution of the additive through theentirety of the continuous phase. In this regard, the present inventorshave discovered that the ratio of the melt flow rate of themicroinclusion additive to the melt flow rate of the matrix polymer istypically from about 0.5 to about 10, in some embodiments from about 1to about 8, and in some embodiments, from about 2 to about 6. Themicroinclusion additive may, for example, have a melt low rate of fromabout 5 to about 200 grams per 10 minutes, in some embodiments fromabout 20 to about 150 grams per 10 minutes, and in some embodiments,from about 40 to about 100 grams per 10 minutes, determined at a load of2160 grams and at a temperature at least about 40° C. above its meltingtemperature (e.g., 210° C.).

In addition to the properties noted above, the mechanicalcharacteristics of the microinclusion additive may also be selected toachieve the desired porous network. For example, applied with anexternal force, stress concentrate (e.g., including normal or shearstresses) and shear and/or plastic yielding zones may be initiated atand around the discrete phase domains as a result of stress concentratethat arise from a difference in the elastic modulus of the additive andmatrix polymer. Larger stress concentrations promote more intensivelocalised plastic flow at the domains, which allows them to becomesignificantly elongated when stresses are imparted. These elongateddomains can allow the composition to exhibit a more pliable and softerbehavior. To enhance the stress concentrations, the microinclusionadditive may be selected to have a relatively high Young's modulus ofelasticity in comparison to the polyolefin matrix. For example, theratio of the modulus of elasticity of the additive to that of polyolefinmatrix is typically from about 1 to about 250, in some embodiments fromabout 2 to about 100, and in some embodiments, from about 2 to about 50.The modulus of elasticity of the microinclusion additive may, forinstance, range from about 200 to about 3,500 Megapascals (MPa), in someembodiments from about 300 to about 2,000 MPa, and in some embodiments,from about 400 to about 1,500 MPa. To the contrary, the modulus ofelasticity of the polyolefin may, for instance, range from about 100 toabout 1,500 MPa, and in some embodiments, from about 200 to about 1000MPa. Alternatively, the modulus of elasticity of microinclusion additivecan be lower than the modulus of elasticity of polyolefin matrix. Themodulus of elasticity may, for example, range from about 10 MPa to about100 MPa, and optionally from about 20 MPA to about 80 MPa.

While a wide variety of microinclusion additives may be employed thathave the properties identified above, particularly suitable examples ofsuch additives may include styrenic copolymers (e.g.,styrene-butadiene-styrene, styrene-isoprene-styrene,styrene-ethylene-propylene-styrene, styrene-ethylene-butadiene-styrene,etc.); fluoropolymers, such as polyvinyl chloride (PVC),polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE),etc.; polyvinyl alcohols; polyvinyl acetates; polyesters, such asaliphatic polyesters, such as polycaprolactone, polyesteramides,polylactic acid (PLA) and its copolymers, polyglycolic acid,polyalkylene carbonates (e.g., polyethylene carbonate),poly-3-hydroxybutyrate (PHB), poly-3-hydroxyvalerate (PHV),poly-3-hydroxybutyrate-co-4-hydroybutyrate,poly-3-hydroxybutyrate-co-3-hydroxyvalerate copolymers (PHBV),poly-3-hydroxybutyrate-co-3-hydroxyhexanoate,poly-3-hydroxybutyrate-co-3-hydroxyoctanoate,poly-3-hydroxybutyrate-co-3-hydroxydecanoate,poly-3-hydroxybutyrate-co-3-hydroxyoctanoate, and succinate-basedaliphatic polymers (e.g., polybutylene succinate, polybutylene succinateadipate, polyethylene succinate, etc.), aliphatic-aromatic copolyesters(e.g., polybutylene adipate terephthalate, polyethylene adipateterephthalate, polyethylene adipate isophthalate, polybutylene adipateisophthalate, etc.), aromatic polyesters (e.g., polyethyleneterephthalate, polybutylene terephthalate, etc.); and so forth.

Particularly suitable are microinclusion additives that are generallyrigid in nature to the extent that they have a relatively high glasstransition temperature. For example, the glass transition temperature(“T_(g)”) may be about 0° C. or more, in some embodiments from about 5°C. to about 100° C., in some embodiments from about 30° C. to about 80°C., and in some embodiments, from about 50° C. to about 75° C. The glasstransition temperature may be determined by dynamic mechanical analysisin accordance with ASTM E1640-09.

One particularly suitable rigid polyester is potylactic acid, which maygenerally be derived from monomer units of any isomer of lactic acid,such as levorotory-lactic acid (“L-lactic acid”), dextrorotatory-lacticacid (“D-lactic acid”), meso-lactic acid, or mixtures thereof. Monomerunits may also be formed from anhydrides of any isomer of lactic acid,including L-lactide, D-lactide, meso-lactide, or mixtures thereof.Cyclic dimers of such lactic acids and/or lactides may also be employed.Any known polymerization method, such as polycondensation orring-opening polymerization, may be used to polymerize lactic acid. Asmall amount of a chain-extending agent (e.g., a diisocyanate compound,an epoxy compound or an acid anhydride) may also be employed. Thepolylactic acid may be a homopolymer or a copolymer, such as one thatcontains monomer units derived from L-lactic acid and monomer unitsderived from D-lactic acid. Although not required, the rate of contentof one of the monomer unit derived from L-lactic acid and the monomerunit derived from D-lactic acid is preferably adeut 85 mole % or more,in some embodiments about 90 mole % or more, and in some embodiments,about 95 mole % or more. Multiple polylactic acids, each having adifferent ratio between the monomer unit derived from L-lactic acid andthe monomer unit derived from D-lactic acid, may be blended at anarbitrary percentage. Of course, polylactic acid may also be blendedwith other types of polymers (e.g., polyolefins, polyesters, etc.).

In one particular embodiment, the polylactic acid has the followinggeneral structure:

One specific example of a suitable polylactic acid polymer that may beused in the present invention is commercially available from Biomer,Inc. of Krailling, Germany) under the name BIOMER™ L9000. Other suitablepolylactic acid polymer are commercially available from Natureworks LLCof Minnetonka, Minn. (NAIUREWORKS®) or Mitsui Chemical (LACEA™). Stillother suitable polylactic acids may be described in U.S. Pat. Nos.4,797,468; 5,470,944; 5,770,682; 5,821,327; 5,880,254; and 6,320,458,which are incorporated herein in their entirety by reference thereto forall purposes.

The polylactic acid typically has a number average molecular weight(“M_(n)”) ranging from about 40,000 to about 180,000 grams per mole, insome embodiments from about 50,000 to about 160,000 grams per mole, andin some embodiments, from about 80,000 to about 120,000 grams per mole.Likewise, the polymer also typically has a weight average molecularweight (“M_(w)”) ranging from about 80,000 to about 250,000 grams permole, in some embodiments from about 100,000 to about 200,000 grams permole, and in some embodiments, from about 110,000 to about 160,000 gramsper mole. The ratio of the weight average molecular weight to the numberaverage molecular weight (“M_(w)/M_(n)”), i.e., the “polydispersityindex”, is also relatively low. For example, the polydispersity indextypically ranges from about 1.0 to about 3.0, in some embodiments fromabout 1.1 to about 2.0, and in some embodiments, from about 1.2 to about1.3. The weight and number average molecular weights may be determinedby methods known to those skilled in the art.

Some types of neat polyesters (e.g., polylactic acid) can absorb waterfrom the ambient environment such that it has a moisture content ofabout 500 to 600 parts per million (“ppm”), or even greater, based onthe dry weight of the starting polylactic acid. Moisture content may bedetermined in a variety of ways as is known in the art, such as inaccordance with ASTM D 7191-05, such as described below. Because thepresence of water during melt processing can hydrolytically degrade thepolyester and reduce its molecular weight, it is sometimes desired todry the polyester prior to binding. In most embodiments, for example, itis desired that the renewable polyester have a moisture content of about300 parts per million (“ppm”) or less, in some embodiments about 200 ppmor less, in some embodiments from about 1 to about 100 ppm prior toblending with the microinclusion additive. Drying of the polyester mayoccur, for instance, at a temperature of from about 50° C. to about 100°C., and in some embodiments, from about 70° C. to about 80° C.

Regardless of the materials employed, the relative percentage of themicroinclusion additive in the thermoplastic composition is selected toachieve the desired properties without significantly impacting theresulting composition. For example, the microinclusion additive istypically employed in an amount of from about 1 wt. % to about 30 wt. %,in some embodiments from about 2 wt. % to about 25 wt. %, and in someembodiments, from about 5 wt. % to about 20 wt. % of the thermoplasticcomposition, based on the weight of the polyolefin matrix employee inthe composition. The concentration of the microinclusion additive in theentire thermoplastic composition may likewise constitute from about 0.1wt. % to about 30 wt. %, in some embodiments from about 0.5 wt. % toabout 25 wt. %, and in some embodiments, from about 1 wt. % to about 20wt. %.

D. Other Components

A wide variety of ingredients may be employed in the composition for avariety of different reasons. For instance, in one particularembodiment, an interphase modifier may be employed in the thermoplasticcomposition to help reduce the degree of friction and connectivitybetween the nanoinclusion and/or microinclusion additives and polyolefinmatrix, and thus enhance the degree and uniformity of debonding. In thismanner, the pores can become distributed in a more homogeneous fashionthroughout the composition. The modifier may be in a liquid orsemi-solid form at room temperature (e.g., 25° C.) so that it possessesa relatively low viscosity, allowing it to be more readily incorporatedinto the thermoplastic composition and to easily migrate to the polymersurfaces. By reducing physical forces at the interfaces of thepolyolefin matrix and the additive, it is believed that the lowviscosity, hydrophobic nature of the modifier can help facilitatedebonding. As used herein, the term “hydrophobic” typically refers to amaterial having a contact angle of wafer in air of about 40° or more,and in some cases, about 60° or more. In contrast, the term“hydrophilic” typically refers to a material having a contact angle ofwater in air of less than about 40°. One suitable test for measuring thecontact angle is ASTM D5725-99 (2008).

Although not required, the interphase modifier may be particularlysuitable in embodiments in which a microinclusion additive is employedand in which the nanoinclusion additive is a solid (e.g., polymericmaterial). Suitable hydrophobic, low viscosity interphase modifiers mayinclude, for instance, the liquids and/or semi-solids referenced above.One particularly suitable interphase modifier is polyether polyol, suchas commercially available under the trade name PLURIOL® WI from BASFCorp. Another suitable modifier is a partially renewable ester, such ascommercially available under the trade name HALLGREEN® IM from Hallstar.

When employed, the interphase modifier may constitute from about 0.1 wt.% to about 20 wt. %, in some embodiments from about 0.5 wt. % to about15 wt. %, and in some embodiments, from about 1 wt. % to about 10 wt. %of the thermoplastic composition, based on the weight of the continuousphase polyolefin matrix. The concentration of the interphase modifier inthe entire thermoplastic composition may likewise constitute from about0.05 wt. % to about 20 wt. %, in some embodiments from about 0.1 wt. %to about 15 wt %, and in some embodiments, from about 0.5 wt. % to about10 wt. %. In the amounts noted above, the interphase modifier has acharacter that enables it to readily migrate to the interfacial surfaceof the polymers and facilitate debonding without disrupting the overallmelt properties of the thermoplastic composition. For example, the meltflow rate of the thermoplastic composition may also be similar to thatof the polyolefin matrix. For example, the melt flow rate of thecomposition (on a dry basis) may be from about 0.1 to about 250 gramsper 10 minutes, in some embodiments from about 0.5 to about 200 gramsper 10 minutes, and in some embodiments, from about 5 to about 150 gramsper 10 minutes, determined at a load or 2160 grams and at 190° C. inaccordance with ASTM D1238.

Compatibilizers may also be employed that improve interfacial adhesionand reduce the interfacial tension between the domain and the matrix,thus allowing the formation of smaller domains during mixing. Examplesof suitable compatibilizers may include, for instance, copolymersfunctionalized with epoxy or maleic anhydride chemical moieties. Anexample of a maleic anhydride compatibilizer ispolypropylene-grafted-maleic anhydride, which is commercially availablefrom Arkema under the trade names Orevac™ 18750 and Orevac™ CA100. Whenemployed, compatibilizers may constitute from about 0.05 wt. % to about10 wt. %, in some embodiments from about 0.1 wt. % to about 8 wt. %, andin some embodiments, from about 0.5 wt. % to about 5 wt. % of thethermoplastic composition, based on the weight of the continuous phasematrix.

Other suitable materials that may also be used in the thermoplasticcomposition, such as catalysts, antioxidants, stabilizers, surfactants,waxes, solid solvents, nucleating agents, particulates, nanofillers, andother materials added to enhance the processability and mechanicalproperties of the thermoplastic composition. Nevertheless, onebeneficial aspect of the present invention is that good properties maybe provided without the need for various conventional additives, such asblowing agents (e.g., chlorofluorocarbons, hydrochlorofluorocarbons,hydrocarbons, carbon dioxide, supercritical carbon dioxide, nitrogen,etc.) and pore-initiating fillers (e.g., calcium carbonate). In fact,the thermoplastic composition may be generally free of blowing agentsand/or pore-initiating fillers. For example, such blowing agents and/orfillers may be present in an amount of no more than about 1 wt. %, insome embodiments no more than about 0.5 wt. %, and in some embodiments,from about 0.001 wt. % to about 0.2 wt. % of the thermoplasticcomposition. Further, due to its stress whitening properties, asdescribed in more detail below, the resulting composition may achieve anopaque color (e.g., white) without the need for conventional pigments,such as titanium dioxide. In certain embodiments, for example, pigmentsmay be present in an amount of no more than about 1 wt. %, in someembodiments no more than about 0.5 wt. %, and in some embodiments, fromabout 0.001 wt. % to about 0.2 wt. % of the thermoplastic composition.

II. Blending

To form the thermoplastic composition, the components are typicallyblended together using any of a variety of known techniques. In oneembodiment, for example, the components may be supplied separately or incombination. For instance, the components may first be dry mixedtogether to form an essentially homogeneous dry mixture, and they maylikewise be supplied either simultaneously or in sequence to a meltprocessing device that dispersively blends the materials. Batch and/orcontinuous melt processing techniques may be employed. For example, amixer/kneader, Banbury mixer, Farrel continuous mixer, single-screwextruder, twin-screw extruder, roll mill, etc., may be utilized to blendand melt process the materials. Particularly suitable melt processingdevices may be a co-rotating, twin-screw extruder (e.g., ZSK-30 extruderavailable from Werner & Pfleiderer Corporation of Ramsey, N.J. or aThermo Prism™ USALAB 16 extruder available from Thermo Electron Corp.,Stone, England). Such extruders may include feeding and venting portsand provide high intensity distributive and dispersive mixing. Forexample, the components may be fed to the same or different feedingports of the twin-screw extruder and melt blended to form asubstantially homogeneous melted mixture. If desired, other additivesmay also be injected into the polymer melt and/or separately fed intothe extruder at a different point along its length.

Regardless of the particular processing technique chosen, the resultingmelt blended composition typically contains nano-scale domains of thenanoinclusion additive and optionally micro-scale domains of themicroinclusion additive. The degree of shear/pressure and heat may becontrolled to ensure sufficient dispersion, but not so high as toadversely reduce the size of the domains so that they are incapable ofachieving the desired properties. For example, blending typically occursat a temperature of from 180° C. to about 300° C., in some embodimentsfrom about 185° C. to about 250° C., and in some embodiments, from about190° C. to about 240° C. likewise, the apparent shear rate during meltprocessing may range from about 10 seconds⁻¹ to about 3000 seconds⁻¹, insome embodiments from about 50 seconds⁻¹ to about 2000 seconds⁻¹, and insome embodiments, from about 100 seconds⁻¹ to about 1200 seconds⁻¹. Theapparent shear rate may be equal to 4Q/R³, where Q is the volumetricflow rate (“m³/s”) of the polymer melt and R is the radius (“m”) of thecapillary (e.g., extruder die) through which the melted polymer flows.Of course, other variables, such as the residence time during meltprocessing, which is inversely proportional to throughput rate, may alsobe controlled to achieve the desired degree of homogeneity.

To achieve the desired shear conditions (e.g., rate, residence time,shear rate, melt processing temperature, etc.), the speed of theextruder screw(s) may be selected with a certain range. Generally, anincrease in product temperature is observed with increasing screw speeddue to the additional mechanical energy input into the system. Forexample, the screw speed may range fern about 50 to about 800revolutions per minute (“rpm”), in some embodiments from about 70 toabout 500 rpm, and in some embodiments, from about 100 to about 300 rpm.This may result in a temperature that is sufficiently high to dispersethe nanoinclusion additive without adversely impacting the size of theresulting domains. The melt shear rate, and in turn the degree to whichthe additives are dispersed, may also be increased through the use ofone or more distributive and/or dispersive mixing elements within themixing section of the extruder. Suitable distributive mixers for singlescrew extruders may include, for instance, Saxon, Dulmage, CavityTransfer mixers, etc. Likewise, suitable dispersive mixers may includeBlister ring, Leroy/Maddock, CRD mixers, etc. As is well known in theart, the mixing may be further improved by using pins in the barrel thatcreate a folding and reorientation of the polymer melt, such as thoseused in Buss Kneader extruders, Cavity Transfer mixers, and VortexIntermeshing Pin (VIP) mixers.

III. Fiber Formation

As used herein, the term “fiber” generally refers to an elongatedextrudate formed by passing a polymer through a forming orifice, such asa die. Unless noted otherwise, the term “fiber” includes bothdiscontinuous fibers having a definite length and substantiallycontinuous filaments. Substantially filaments may, for instance, have alength much greater than their diameter, such as a length to diameterratio (“aspect ratio”) greater than about 15,000 to 1, and in somecases, greater than about 50,000 to 1. The fiber is “hollow” to such anextent that it contains a hollow cavity extending along at least aportion of the fiber in the longitudinal direction. In some cases, thecavity may extent along the entire length of the fiber.

As discussed above, the cavity is defined by an interior wall that is,at least in part, formed by the thermoplastic composition of the presentinvention. In certain embodiments, the fiber may be a monocomponentfiber such that the interior wall is formed entirely by thethermoplastic composition. Of course, in other embodiments, the fibermay contain one or more additional polymer layers as a component (e.g.,bicomponent) to further enhance strength, processibility, and/or otherproperties. Such fibers may, for example, have a sheath-coreconfiguration, side-by-side configuration, segmented pie configuration,island-in-the-sea configuration, and so forth. In one particularembodiment, for example, the thermoplastic composition may form a corecomponent of a sheath/core bicomponent fiber, while an additionalpolymer may form the sheath component, or vice versa. The additionalpolymer may be any polymer desired, such as polyesters (e.g., polylacticacid, polyethylene terephthalate, etc.); polyolefins (e.g.,polyethylene, polypropylene, polybutylene, etc.);polytetrafluoroethylone; polyvinyl acetate; polyvinyl chloride acetate;polyvinyl butyral; acrylic resins (e.g., polyacrylate,polymethylacrylate, polymethylmethacrylate, etc.); polyamides (e g.,nylon); polyvinyl chloride; polyvinylidene chloride; polystyrene;polyvinyl alcohol; polyurethanes; and so forth.

Regardless of their particular configuration, any of a variety ofprocesses may be used to form the hollow fibers of the presentinvention. For instance, the hollow fibers may be formed using a processin which the thermoplastic composition is extruded through a die system(or spinneret) that may include a housing containing a spin pack havinga plurality of plates stacked one on top of each other and having apattern of capillaries arranged to create flow paths for directing thethermoplastic composition. Referring to FIG. 2, for example, oneembodiment of a method for forming fibers is shown in more detail. Inthis particular embodiment, the thermoplastic composition of the presentinvention may be fed into an extruder 12 from a hopper 14. The blend maybe provided to the hopper 14 using any conventional technique. Theextruder 12 heated to a temperature sufficient to extrude the meltedpolymer. To help limit deterioration of the hollow cavity as if isformed, the composition is typically melt spun at a temperature of fromabout 180° C. to about 300° C., in some embodiments from about 200° C.to about 260° C., and in some embodiments, from about 210° C. to about250° C.

The extruded composition is then passed through a polymer conduit 16 toa spinneret 18. If desired, the particular nature of the spinneret 18can be selectively controlled in the present invention to assist in theformation of a hollow cavity in the fibers. In certain embodiments, forinstance, a gaseous fluid (e.g., air, inert gas, etc.) may be passedthrough the composition as it is pumped through a capillary to impart ahollow configuration to the resulting fiber. For example, the gaseousfluid can be passed through a needle that extends into a central portionof the capillary. Examples of this technique are described, forinstance, in U.S. Pat. No. 4,405,688 to Lowery, et al.; U.S. Pat. No.5,662,671 to Pellegrin, et al.; and U.S. Pat. No. 6,642,429 to Carter,et al. In many cases, however, the use of such a gaseous fluid may beundesirable as if tends to lead to a hollow cavity that lacks uniformityand consistency. Thus, in alternative embodiments of the presentinvention, the hollow fiber may be formed by passing the compositionthrough a capillary within which one more shaped slots or segments arepositioned. For example, the slots may have a multi-directional shape(e.g., C-shaped, arc-shaped, etc.) so that the composition forms a bulgewhen passed therethrough, which causes it coalesces a short distancebelow the face of the die and thereby form a fiber with a hollowinterior. Referring to FIGS. 3-4, for instance, one embodiment aspinneret is shown that can be used to form hollow fibers of the presentinvention. The spinneret contains a capillary 116 that extends through aplate 110 from a surface 112 to a face 114. In this particularembodiment, the capillary 116 has an entrance hole 118 that communicateswith individual slots 120, 122, 124 and 126 through entrances 121, 123,125 and 127, respectively.

In any event, referring again to FIG. 2, the spinneret 18 also hasopenings arranged in one or more rows. The openings form a downwardlyextruding curtain of filaments when the polymers are extrudedtherethrough. The process 10 also employs a quench blower 20 positionedadjacent the curtain of fibers extending from the spinneret 18. Air tornthe quench air blower 20 quenches the fibers extending from thespinneret 18. The quench air may be directed from one side of the fibercurtain as shown in FIG. 2 or both sides of the fiber curtain. To form afiber with the desired length, the quenched fibers are generally meltdrawn, such as using a fiber draw unit 22 as shown in FIG. 2. Fiber drawunits or aspirators for use in melt spinning polymers are well-known inthe art. Suitable fiber draw units for use in the process of the presentinvention include a linear fiber aspirator of the type shown in U.S.Pat. Nos. 3,802,817 and 3,423,255. The fiber draw 22 generally includesan elongated vertical passage through which the fibers are drawn byaspirating air entering from the sides of the passage and flowingdownwardly through the passage. A heater or blower 24 suppliesaspirating air to the fiber draw unit 22. The aspirating air melt drawsthe fibers and ambient air through the fiber draw unit 22. The flow ofgas causes the fibers to melt draw or attenuate, which increases themolecular orientation or crystallinity of the polymers forming thefibers. When employing a fiber draw unit, the “draw down” ratio may beselected to help achieve the desired fiber length. The “drawn down”ratio is the linear speed of the fibers after drawing (e.g., linearspeed of the godet roll 42 or a foraminous surface (not shown) dividedby the linear speed of the fibers after extrusion). For example, thedraw down ratio during melt drawing may be calculated as follows:Draw Down Ratio=A/Bwherein,

A is the linear speed of the fiber after melt drawing (e.g., godetspeed) and is directly measured; and

B is the linear speed of the extruded fiber and can be calculated asfollows:Extruder linear fiber speed=C/(25*π*D*E ²)wherein,

C is the throughput through a single hole (grams per minute);

D is the melt density of the polymer (grams per cubic centimeter); and

E is the diameter of the orifice (in centimeters) through which thefiber is extruded. In certain embodiments, the draw down ratio may befrom about 5:1 to about 4000:1, in some embodiments from about 10:1 toabout 2000:1, and in some embodiments, from about 15:1 to about 1000:1and in some embodiments from about 20:1 to about 800:1.

Once formed, the fibers may be deposited through the outlet opening ofthe fiber draw unit 22 and onto a godet roll 42. If desired, the fiberscollected on the godet roll 42 may optionally be subjected to additionalin line processing and/or converting steps (not shown) as will beunderstood by those skilled in the art. For example, fibers may becollected and thereafter crimped, texturized, and/or cut to an averagefiber length in the range of from about 3 to about 80 millimeters, insome embodiments from about 4 to about 65 millimeters, and in someembodiments, from about 5 to about 50 millimeters. The staple fibers maythen be incorporated into a nonwoven web as is known in the art, such asbonded carded webs, through-air bonded webs, etc. The fibers may also bedeposited onto a foraminous surface to form a nonwoven web, such asdescribed in more detail below.

Regardless of the particular manner in which they are formed, theresulting fibers may be drawn to form the desired porous network. Ifdesired, the fibers may be drawn in-line as the fibers are being formed.Alternatively, the fibers may be drawn in their solid state after theyare formed. By “solid state” drawing, it is generally meant that thecomposition is kept at a temperature below the melting temperate of thepolyolefin matrix polymer. Among other things, this helps to ensure thatthe polymer chains are not altered to such an extent that the porousnetwork becomes unstable. For example, the composition may be drawn at atemperature of from about −50° C. to about 150° C., in some embodimentsfmm about −40° C. to about 100° C., in some embodiments from about −20°C. to about 50° C., and in some embodiments, from about 20° C. to about50° C. This may optionally be at least about 10° C., in some embodimentsat least about 20° C., and in some embodiments, at least about 30° C.below the glass transition temperature of the component having thehighest glass transition temperature (e.g., microinclusion additive).

Drawing of the fibers may occur in one or multiple stages. In oneembodiment, for example, drawing is completed in-line without having toremove it for separate processing. In FIG. 2, for instance, the fibersmay be initially melt drawn by the fiber draw unit 22, transferred to anip (not shown) where the matrix polymer is allowed to cool below itsmelting temperature, and thereafter subjected to an additional drawingstep before being deposited on the godet roll 42. In other cases,however, the fibers may be removed from the fiber forming machinery andsubjected to an additional drawing step. Regardless, various drawingtechniques may be employed, such as aspiration (e.g., fiber draw units),tensile frame drawing, biaxial drawing, multi-axial drawing, profiledrawing, vacuum drawing, etc. The composition is typically drawn (e.g.,in the machine direction) to a draw ratio of from about 1.1 to about 25,in some embodiments from about 1.5 to about 15, and in some embodiments,from about 2 to about 10. The draw ratio may be determined by dividingthe length of the drawn fiber by its length before drawing. The drawrate may also vary to help achieve the desired properties, such aswithin the range of from about 5% to about 1500% per minute ofdeformation, in some embodiments from about 20% to about 1000% perminute of deformation, and in some embodiments, front about 25% to about850% per minute of deformation. Although the composition is typicallydrawn without the application of external heat (e.g., heated roils),such heat might be optionally employed to improve processability, reducedraw force, increase draw rates, and improve fiber uniformity.

Drawing in the manner described above can result in the formation ofpores having a “nano-scale” dimension (“nanopores”), such as an averagecross-sectional dimension of about 800 nanometers or less, in someembodiments from about 5 to about 700 nanometers, and in someembodiments, from about 10 to about 500 nanometers. The nanopores mayalso have an average axial dimension (e.g., length) of from about 100 toabout 5000 nanometers, in some embodiments from about 50 to about 2000nanometers, and in some embodiments, from about 100 to about 1000nanometers. Micropores may also be formed during drawing that have anaverage cross-sectional dimension of about 0.2 micrometers or more, insome embodiments about 0.5 micrometers or more, and in some embodiments,from about 0.5 micrometers to about 5 micrometers. In certain cases, theaxial dimension of the micropores and/or nanopores may be larger thanthe cross-sectional dimension so that the aspect ratio (the ratio of theaxial dimension to the cross-sectional dimension) is from about 1 toabout 30, in some embodiments from about 1.1 to about 15, and to someembodiments, from about 1.2 to about 5. For example, the axial dimensionof the micropores may be 1 micrometer or more, in some embodiments about1.5 micrometers or more, and in some embodiments, from about 2 to about30 micrometers.

Regardless of their particular size, the present inventors havediscovered that the pores (e.g., nanopores, micropores, or both) can bedistributed in a substantially homogeneous fashion throughout thecomposition. For example, the pores may be distributed in columns thatare oriented in a direction generally perpendicular to the direction inwhich a stress is applied. These columns may be generally parallel toeach other across the width of the composition. Without intending to belimited by theory, it is believed that the presence of such ahomogeneously distributed porous network can result in good mechanicalproperties (e.g., energy dissipation under load and impact strength).This is in stark contrast to conventional techniques for creating poresthat involve the use of blowing agents, which tend to result in anuncontrolled pore distribution and poor mechanical properties.

In addition to forming a porous network, drawing can also significantlyincrease the axial dimension of certain of the discrete domains so thatthey have a generally linear, elongated shape. For example, theelongated micro-scale domains may have an axial dimension that is about10% or more, in some embodiments from about 20% to about 500%, and insome embodiments, from about 50% to about 250% greater than the axialdimension of the domains prior to drawing. The axial dimension (e.g.,length) after drawing may, for instance, range from about 1 μm to about400 μm, in some embodiments from about 5 μm to about 200 μm, and in someembodiments from about 10 μm to about 150 μm. The micro-scale domainsmay also be relatively thin and thus have a small cross-sectionaldimension, such as from about 0.02 to about 20 micrometers, in someembodiments from about 0.1 to about 10 micrometers, and in someembodiments, from 0.4 to about 5 micrometers. This may result in anaspect ratio for the domains (the ratio of the axial dimension to adimension orthogonal to the axial dimension) of from about 2 to about150, in some embodiments from about 3 to about 100, and in someembodiments, from about 4 to eboMt 50. Due to their small size, thenano-scale domains are not typically elongated in the same manner as themicro-scale domains. Thus, the nano-scale domains may retain an averageaxial dimension (e.g., length) of from about 1 to about 1000 nanometers,in some embodiments from about 5 to about 800 nanometers, in someembodiments from about 10 to about 500 nanometers, and in someembodiments from about 20 to about 200 nanometers.

Drawing may also create one or more localized necked regions along thelongitudinal direction of the fiber, which are spaced between unneckedregions. The necked fibers may also possess a non-uniform,cross-sectional diameter along its longitudinal direction, which canprovide a variety of different benefits, such as increased surface area,etc. The number of necked regions may generally vary and may becontrolled based on the selected stretch ratio. Typically, however, thenumber of necked regions may range from about 1 to about 400 necks percentimeter, in some embodiments from about 2 to about 200 necks percentimeter, and in some embodiments, from about 5 to about 50 necks percentimeter. The number of necked regions may be determined from thefollowing equation:N=(1−L ₂)/(L ₁ +L ₂)

where, N is the number of necked regions, L₁ is the average length of anecked region, and L₂ is the average length of an unnecked region(includes transition from necked to unnecked region.

Even at the very low densities achieved by the present invention, theresulting fibers are not brittle and thus can deform upon theapplication of strain, rather than fracture. The fibers may thuscontinue to function as a load bearing member even after the fiber hasexhibited substantial elongation. In this regard, the fibers of thepresent invention are capable of exhibiting improved “peak elongationproperties, i.e., the percent elongation of the fiber at its peak load.For example, the fibers of the present invention may exhibit a peakelongation of about 50% or more, in some embodiments about 100% or more,in some embodiments from about 200% to about 1500%, and in someembodiments, from about 400% to about 800%, such as determined inaccordance with ASTM D638-10 at 23° C. Such elongations may be achievedfor fibers having a wide variety of average diameters, such as thoseranging from about 0.1 to about 50 micrometers, in some embodiments fromabout 1 to about 40 micrometers, in some embodiments from about 2 toabout 25 micrometers, and in some embodiments, from about 5 to about 15micrometers.

While possessing the ability to extend under strain, the fibers of thepresent invention can also remain relatively strong. For example, thefibers may exhibit a peak tensile stress of from about 25 to about 600Megapascals (“MPa”), in some embodiments from about 50 to about 450 MPa,and in some embodiments, from about 60 to about 350 MPa, such asdetermined in accordance with ASTM D638-10 at 23° C. Another parameterthat is indicative of the relative strength of the fibers of the presentinvention is “tenacity”, which indicates the tensile strength of a fiberexpressed as force per unit linear density. For example, the fibers ofthe present invention may have a tenacity of from about 0.75 to about7.0 grams-force (“g_(f)”) per denier, in some embodiments from about 1.0to about 6.0 g_(f) per denier, and in some embodiments, from about 1.5to about 5.0 g_(f) per denier. The denier of the fibers may varydepending on the desired application. Typically, the fibers are formedto have a denier per filament (i.e., the unit of linear density equal tothe mass in grams per 9000 meters of fiber) of less than about 15, insome embodiments less than about 12, and in some embodiments, from about0.5 to about 6.

III. Nonwoven Web

The hollow fibers of the present invention possess can be suitablyemployed in various applications without first being formed into anytype of coherent structure. Nevertheless, in certain cases, it may bedesired to form the fibers into a coherent nonwoven web structure byrandomly depositing the fibers onto a forming surface (optionally withthe aid of a vacuum) and then bonding the resulting web using any knowntechnique. The nonwoven web may be formed before or after the fibers aredrawn. In certain embodiments, for instance, it may be desired to form anonwoven web from a plurality of fibers, and thereafter draw the fibersby stretching the nonwoven web to the extent desired to form the porousnetwork. In an alternative embodiment, an endless forming surface maysimply be positioned below a fiber aspiration unit that draws the fibersto the desired extent before the web is formed.

Once formed, the nonwoven web may then be bonded using any conventionaltechnique, such as with an adhesive or autogenously (e.g., fusion and/orself-adhesion of the fibers without an applied external adhesive).Autogenous bonding, for instance, may be achieved through contact of thefibers while they are semi-molten or tacky, or simply by blending atackifying resin and/or solvent with the polymer used to form thefibers. Suitable autogenous bonding techniques may include ultrasonicbonding, thermal bonding, through-air bonding, calendar bonding, and soforth. For example, the web may be further bonded or embossed with apattern by a thermo-mechanical process in which the web is passedbetween a heated smooth anvil roll and a heated pattern roll. Thepattern roll may have any raised pattern which provides the desired webproperties or appearance. Desirably, the pattern roll defines a raisedpattern which defines a plurality of bond locations which define a bondarea between about 2% and 30% of the total area of the roll. Exemplarybond patterns include, for instance, those described in U.S. Pat. No.3,855,046 to Hansen et al., U.S. Pat. No. 5,620,770 to Levy et al., U.S.Pat. No. 5,962,112 to Haynes et al., U.S. Pat. No. 6,093,665 to Savovitzet al., as well as U.S. Design Pat. Nos. 428,267 to Romano et al.;380,708 to Brown; 418,305 to Zander et al.; 384,508 to Zander, et al.;384,819 to Zander, et al.; 358,035 to Zander, et al.; and 315,990 toBlenke, et al. The pressure between the rolls may be from about 6 toabout 2000 pounds per lineal inch. The pressure between the rolls andthe temperature of the rolls is balanced to obtain desired webproperties or appearance while maintaining cloth like properties. As iswell known to those skilled in the art, the temperature and pressurerequired may vary depending upon many factors including but not limitedto, pattern bond area, polymer properties, fiber properties and nonwovenproperties.

In addition to spunbond webs, a variety of other nonwoven webs may alsobe formed from the thermoplastic composition in accordance with thepresent invention, such as meltblown webs, bonded carded webs, wet-laidwebs, airlaid webs, coform webs, hydraulically entangled webs, etc. Forexample, the thermoplastic composition may be extruded through aplurality of line die capillaries into a converging high velocity gas(e.g., air) streams that attenuate the fibers to reduce their diameter.Thereafter, the meltblown fibers are carried by the high velocity gasstream and are deposited on a collecting surface to form a web ofrandomly dispersed meltblown fibers. Alternatively, the polymer may beformed into a carded web by placing bales of fibers formed from thethermoplastic composition into a picker that separates the fibers. Next,the fibers are sent through a combing or carding unit that furtherbreaks apart and aligns the fibers in the machine direction so as toform a machine direction-oriented fibrous nonwoven web. Once formed, thenonwoven web is typically stabilized by one or more known bondingtechniques as described above to form a bonded carded web.

If desired, the nonwoven web may also be a composite that contains acombination of the fibers of the present invention and other types offibers (e.g., staple fibers, filaments, etc.). For example, additionalsynthetic fibers may be utilized, such as those formed from polyolefins,e.g., polyethylene, polypropylene, polybutylene, and so forth;polytetefluoroethylene; polyesters, e.g., polyethylene terephthalate andso forth; polyvinyl acetate; polyvinyl chloride acetate; polyvinylbutyral; acrylic resins, e.g., polyacrylate, polymethylacrylate,polymethylmethacrylate, and so forth; polyamides, e.g., nylon; polyvinylchloride; polyvinylidene chloride; polystyrene; polyvinyl alcohol;polyurethanes; polylactic acid; etc. If desired, renewable polymers mayalso be employed. Some examples of known synthetic fibers includesheath-core bicomponent fibers available from KoSa Inc. of Charlotte,N.C. under the designations T-255 and T-256, both of which use apolyolefin sheath, or T-254, which has a low melt co-polyester sheath.Still other known bicomponent fibers that may be used include thoseavailable from the Chisso Corporation of Moriyama, Japan or FibervisionsLLC of Wilmington, Del. Polylactic acid staple fibers may also beemployed, such as those commercially available from Far Eastern Textile,Ltd. of Taiwan.

The composite may also contain pulp fibers, such as high-average fiberlength pulp, low-average fiber length pulp, or mixtures thereof. Oneexample of suitable high-average length fluff pulp fibers includessoftwood kraft pulp fibers. Softwood kraft pulp fibers are derived fromconiferous trees and include pulp fibers such as, but not limited to,northern, western, and southern softwood species, including redwood, redcedar, hemlock, Douglas fir, true firs, pine (e.g., southern pines),spruce (e.g., black spruce), bamboo, combinations thereof, and so forth.Northern softwood kraft pulp fibers may be used in the presentinvention. An example of commercially available southern softwood kraftpulp fibers suitable for use in the present invention include thoseavailable from Weyerhaeuser Company with offices in Federal Way, Wash.under the trade designation of “NF-405.” Another suitable pulp for usein the present invention is a bleached, sulfate wood pulp containingprimarily softwood fibers that is available from Bowater Corp. withoffices in Greenville, S.C. under the trade name CoosAbsorb S pulp.Low-average length fibers may also be used in the present invention. Anexample of suitable low-average length pulp fibers is hardwood kraftpulp fibers. Hardwood kraft pulp fibers are derived from deciduous treesand include pulp fibers such as, but not limited to, eucalyptus, maple,birch, aspen, etc. Eucalyptus kraft pulp fibers may be particularlydesired to increase softness, enhance brightness, increase opacity, andchange the pore structure of the sheet to increase its wicking ability.Bamboo or cotton fibers may also be employed.

Nonwoven composites may be formed using a variety of known techniques.For example, the nonwoven composite may be a “coform material” thatcontains a mixture or stabilized matrix of the thermoplastic compositionfibers and an absorbent material. As an example, coform materials may bemade by a process in which at least one meltblown die head is arrangednear a chute through which the absorbent materials are added to the webwhile if is forming. Such absorbent materials may include, but are notlimited to, pulp fibers, superabsorbent particles, inorganic and/ororganic absorbent materials, treated polymeric staple fibers, and soforth. The relative percentages of the absorbent material may vary overa wide range depending on the desired characteristics of the nonwovencomposite. For example, the nonwoven composite may contain from about 1wt. % to about 60 wt. %, in some embodiments from 5 wt. % to about 50wt. %, and in some embodiments, from about 10 wt. % to about 40 wt. %thermoplastic composition fibers. The nonwoven composite may likewisecontain from about 40 wt. % to about 99 wt. %, in some embodiments from50 wt. % to about 95 wt. %, and in some embodiments, from about 60 wt. %to about 90 wt. % absorbent material. Some examples of such coformmaterials are disclosed in U.S. Pat. No. 4,100,324 to Anderson, et al.;U.S. Pat. No. 5,284,703 to Everhart, et al.; and U.S. Pat. No. 5,350,624to Georger, et al.

Nonwoven laminates may also be formed in the present invention in whichone or more layers are formed from the thermoplastic composition. Forexample, the nonwoven web of one layer may be a spunbond that containsthe thermoplastic composition, while the nonwoven web of another layercontains thermoplastic composition, other renewable polymer(s), and/orany other polymer (e.g., polyolefins). In one embodiment, the nonwovenlaminate contains a meltblown layer positioned between two spunbondlayers to form a spunbond/meltblown/spunbond (“SMS”) laminate. Ifdesired, the spunbond layer(s) may be formed from the thermoplasticcomposition. The meltblown layer may be formed from the thermoplasticcomposition, other renewable polymer(s), and/or any other polymer (e.g.,polyolefins). Various techniques for forming SMS laminates are describedin U.S. Pat. No. 4,041,203 to Brock et al.; U.S. Pat. No. 5,213,881 toTimmons, et al.; U.S. Pat. No. 5,464,688 to Timmons, et al.; U.S. Pat.No. 4,374,888 to Bornslaeger; U.S. Pat. No. 5,169,706 to Collier, etal.; and U.S. Pat. No. 4,766,029 to Brock et al., as well as U.S. PatentApplication Publication No. 2004/0002273 to Fitting, et al. Of course,the nonwoven laminate may have other configuration and possess anydesired number of meltblown and spunbond layers, such asspunbond/meltblown/meltdown/spunbond laminates (“SMMS”),spunbond/meltblown laminates (“SM”), etc. Although the basis weight ofthe nonwoven laminate may be tailored to the desired application, itgenerally ranges from about 10 to about 300 grams per square meter(“gsm”), in some embodiments from about 25 to about 200 gsm, and in someembodiments, from about 40 to about 150 gsm.

Nonwoven-film laminates may also be formed. In such embodiments, thefilm is typically liquid-impermeable and either vapor-permeable orvapor-impermeable. Films that are liquid-impermeable and vapor-permeableare often referred to as “breathable” and they typically have a watervapor transmission rate (“WVTR”) of about 100 grams per square meter per24 hours (g/m²/24 hours) or more, in some embodiments from about 500 toabout 20,000 g/m²/24 hours, and in some embodiments, from about 1,000 toabout 15,000 g g/m²/24 hours. The breathable film may also be amicroporous or monolithic film. Microporous films are typically formedby incorporating a filler (e.g., calcium carbonate) into the polymermatrix, and thereafter stretching the film to create the pores. Examplesof such films are described, for instance, in U.S. Pat. No. 5,843,057 toMcCormack; U.S. Pat. No. 5,855,999 to McCormack; U.S. Pat. No. 5,932,497to Morman, et al.; U.S. Pat. No. 5,997,981 to McCormack, et al.; U.S.Pat. No. 6,002,064 to Kobylivker, et al.; U.S. Pat. No. 6,015,764 toMcCormack et al.; U.S. Pat. No. 6,037,281 to Mathis, et al.; U.S. Pat.No. 6,111,163 to McCormack, et al.; and U.S. Pat. No. 6,461,457 toTaylor, et al.

If desired, the fibers, nonwoven web, etc., may also be annealed to helpensure that they retains the desired shape. Annealing typically occursat temperatures of from about 40° C. to about 120° C., in someembodiments from about 50° C. to about 110° C., and in some embodiments,from about 80° C. to about 100° C. The fibers may also be surfacetreated using any of a vanety of known techniques to improve itsproperties. For example, high energy beams (e.g., plasma, x-rays,e-beam, etc.) may be used to remove or reduce any skin layers that formon the fibers, to change the surface polarity, embrittle a surfacelayer, etc. If desired, such surface treatment may be used before and/orafter formation of a web, as well as before and/or after cold drawing ofthe fibers.

Besides a reduced density, the nanoporous structure may also provide avariety of additional different benefits to the nonwoven web containingthe polyolefin fibers of the present invention. For example, thenanoporous structure can help restrict the flow of fluids and begenerally impermeable to fluids (e.g., liquid water), thereby allowingthe nonwoven web to insulate a surface from water penetration. In thisregard, the fibrous material may have a relatively high hydrohead valueof about 50 centimeters (“cm”) or more, in some embodiments about 100 cmor more, in some embodiments, about 150 cm or more, and in someembodiments, from about 200 cm to about 1000 cm, as determined inaccordance with ATTCC 127-2008. Other beneficial properties may also beachieved. For example, the nonwoven web may be generally permeable towater vapors. The permeability of a fibrous material to water vapor maycharacterized by its relatively high water vapor transmission rate(“WVTR”), which is the rate at which water vapor permeates through amaterial as measured in units of grams per meter squared per 24 hours(g/m²/24 hrs). For example, the nonwoven web may exhibit a WVTR of about300 g/m²-24 hours or more, in some embodiments about 500 g/m²-24 hoursor more, in some embodiments about 1,000 g/m²-24 hours or more, and insome embodiments, from about 3,000 to about 15,000 g/m²-24 hours, suchas determined in accordance with ASTM E96/96M-12, Procedure B or INDATest Procedure IST-70.4 (01).

IV. Articles

The hollow fibers of the present invention may be employed in a widevariety of different articles. Due to their unique porous nature, forinstance, the hollow fibers can be employed in wafer purificationmembranes, blood oxygenators, desalination equipment, membranedistillation equipment, absorbent articles, etc. In one embodiment, forinstance, the hollow fibers can be used to assist in blood oxygenation.In such embodiments, it may be desired to form a bundle of the hollowfibers, which may then be inserted into an elongated tubular casingassembly so that blood can be pumped through the hollow fibers. Oxygengas can then pass through the external walls of the hollow fibers andoxygenate the blood passing within the fiber while carbon dioxide ispassed out of the blood through the hollow fiber. Alternatively, oxygengas may be passed into the center of the hollow fibers and the bloodcirculated through the casing thereby contacting the external surface ofthe hollow fibers. Rather than utilizing a dual-ended tubular casing inwhich both ends are open to allow the passage of blood, it is possibleto utilize a permeator in which hollow fiber bundles are formed into aloop so that the ends of each of the fibers both exit through the sameopening in the tubular casing. Examples of such devices are described inU.S. Pat. Nos. 2,972,349; 3,373,876; and 4,031,012.

In other embodiments, the hollow fibers may be employed in an absorbentarticle. An absorbent article that is capable of absorbing water orother fluids. Examples of some absorbent articles include, but are notlimited to, personal care absorbent articles, such as diapers, trainingpants, absorbent underpants, adult incontinence articles, femininehygiene products, (e.g., sanitary napkins), swim wear, baby wipes, mittwipes, and so forth; medical absorbent articles, such as garments,fenestration materials, underpads, bandages, absorbent drapes, andmedical wipes; food service wipers; clothing articles; and so forth.Regardless of the intended application, the absorbent article typicallycontains an absorbent member (e.g., core layer, surge layer, transferdelay layer, wrapsheet, ventilation layer, etc.) positioned between abacsheet and a topsheet. Notably, the absorbent member, backsheet,and/or topsheet as well one or more other components of the absorbentarticle (e.g., ears, containment flaps, side panels, waist or leg bands,etc.) may include the hollow fibers of foe present invention, eitheralone or in the form of a nonwoven web containing such fibers.

In this regard, various exemplary embodiments of the absorbent articlewill be described. Referring to FIG. 1, for instance, one particularembodiment of an absorbent article 201 is shown in the form of a diaper.However, as noted above, the invention may be embodied in other types ofabsorbent articles, such as incontinence articles, sanitary napkins,diaper pants, feminine napkins, training pants, and so forth. In theillustrated embodiment, the absorbent article 201 is shown as having anhourglass shape in an unfastened configuration. However, other shapesmay of course be utilized, such as a generally rectangular shape,T-shape, or I-shape. As shown, the absorbent article 201 includes achassis 202 formed by various components, including a backsheet 217,topsheet 205, and absorbent member that includes an absorbent core layer203 and surge layer 207. It should be understood, however, that otherlayers may also be used in the present invention. Likewise, one or moreof the layers referred to in FIG. 1 may also be eliminated in certainembodiments of the present invention.

As indicated above, the backsheet 217 may contain the hollow fibers ofthe present invention, optionally in the form of a nonwoven web. Forexample, the nonwoven web may be positioned so that it defines agarment-facing surface 333 of the absorbent article 201. The absorbentarticle 201 also includes a topsheet 205. The topsheet 205 is generallydesigned to contact the body of the user and is liquid-permeable. Forexample, the topsheet 205 may define a body-facing surface 218, which istypically compliant, soft feeling, and non-irritating to the wearersskin. If desired, the topsheet 205 may contain the hollow fibers of thepresent invention, optionally in the form of a nonwoven web. Forexample, a nonwoven web may be positioned so that it defines thebody-facing surface 218 if so desired. The topsheet may surround theabsorbent core layer 203 so that it completely encases the absorbentarticle. Alternatively, the top-sheet 205 and the backsheet 217 mayextend beyond the absorbent member and be peripherally joined together,either entirely or partially, using known techniques, such as byadhesive bonding, ultrasonic bonding, etc. As indicated above, thetopsheet 205 may include the nonwoven web of the present invention. Thetopsheet 205 may also include a conventional a nonwoven web (e.g.,spunbond web, meltblown web, or bonded carded web). Other exemplarytopsheet constructions that contain a nonwoven web are described in U.S.Pat. Nos. 5,192,606; 5,702,377; 5,931,823; 6,060,638; and 6,150,002, aswell as U.S. Patent Application Publication Nos. 2004/0102750,2005/0054255, and 2005/0059941. The topsheet 205 may also contain aplurality of apertures formed therethrough to permit body fluid to passmore readily into the absorbent core layer 203. The apertures may berandomly or uniformly arranged throughout the topsheet 205, or they maybe located only in the narrow longitudinal band or strip arranged alongthe longitudinal axis of the absorbent article. The apertures permitrapid penetration of body fluid down into the absorbent member. Thesize, shape, diameter and number of apertures may be varied to suitone's particular needs.

The absorbent article also contains an absorbent member positionedbetween the topsheet and the backsheet. The absorbent member may beformed from a single absorbent layer or a composite containing separateand distinct absorbent layer. It should be understood, however, that anynumber of absorbent layers may be utilized in the present invention. InFIG. 1, for instance, the absorbent member contains an absorbent corelayer 203 and a surge layer 207 that helps to decelerate and diffusesurges or gushes of liquid that may be rapidly introduced into theabsorbent core layer 203. Desirably, the surge layer 207 rapidly acceptsand temporarily holds the liquid prior to releasing it into the storageor retention portions of the absorbent core layer 203. In theillustrated embodiment, for example, the surge layer 207 is interposedbetween an inwardly facing surface 216 of the topsheet 205 and theabsorbent core layer 203. Alternatively, the surge layer 207 may belocated on the outwardly facing surface 218 of the topsheet 205. Thesurge layer 207 is typically constructed from highly liquid-permeablematerials. Suitable materials may include porous woven materials, porousnonwoven materials, and apertured films. In one embodiment, the surgelayer 207 may contain the hollow fibers of the present invention,optionally in the form of a nonwoven web. Other examples of suitablesurge layers are described in U.S. Pat. No. 5,486,166 to Ellis, et al.and U.S. Pat. No. 5,490,846 to Ellis, et al.

If desired, the absorbent member may also contain a transfer delay layerpositioned vertically below the surge layer. The transfer delay layermay contain a material that is less hydrophilic than the other absorbentlayers, and may generally be characterized as being substantiallyhydrophobic. For example, the transfer delay layer may be a nonwoven web(e.g., spunbond web) formed from the hollow fibers of the presentinvention. The fibers may be round, tri-lobel or poly-lobal incross-sectional shape and which may be hollow or solid in structure.Typscally the webs are bonded, such as by thermal bonding, over about 3%to about 30% of the web area. Other examples of suitable materials thatmay be used for the transfer delay layer are described in U.S. Pat. No.4,798,603 to Meyer, et al. and U.S. Pat. No. 5,248,309 to Serbiak, etal. To adjust the performance of the invention, the transfer delay layermay also be treated with a selected amount of surfactant to increase itsinitial wettability.

The transfer delay layer may generally have any size, such as a lengthof about 150 mm to about 300 mm. Typically, the length of the transferdelay layer is approximately equal to the length of the absorbentarticle. The transfer delay layer may also be equal in width to thesurge layer, but is typically wider. For example, the width of thetransfer delay layer may be from between about 50 mm to about 75 mm, andparticularly about 48 mm. The transfer delay layer typically has a basisweight less than that of the other absorbent members. For example, thebasis weight of the transfer delay layer is typically less than about150 grams per sgyare meter (gsm), and in some embodiments, between about10 gsm to about 100 gsm. If desired, the transfer delay layer maycontain the hollow fibers of the present invention, optionally in theform of a nonwoven web.

Besides the above-mentioned components, the absorbent article 201 mayalso contain various other components as is known in the art. Forexample, the absorbent article 201 may also contain a substantiallyhydrophilic wrapsheet (not illustrated) that helps maintain theintegrity of the fibrous structure of the absorbent core layer 203. Thewrapsheet is typically placed about the absorbent core layer 203 over atleast the two major facing surfaces thereof, and composed of anabsorbent cellulosic material, such as creped wadding or a highwet-strength tissue. The wrapsheet may be configured to provide awicking layer that helps to rapidly distribute liquid over the mass ofabsorbent fibers of the absorbent core layer 203. The wrapsheet materialon one side of the absorbent fibrous mass may be bonded to the wrapsheetlocated on the opposite side of the fibrous mass to effectively entrapthe absorbent core layer 203. Furthermore, the absorbent article 201 mayalso include a ventilation layer (not shown) that is positioned betweenthe absorbent core layer 203 and the backsheet 217. When utilized, theventilation layer may help insulate the backsheet 217 from the absorbentcore layer 203, thereby reducing dampness in the backsheet 217. Examplesof such ventilation layers may include a nonwoven web laminated to abreathable film, such as described in U.S. Pat. No. 6,663,611 to Blaney,et al. If desired, the wrapsheet and/or ventilation layer may containthe hollow fibers of the present invention, optionally in the form of anonwoven web.

In some embodiments, the absorbent article 201 may also include a pairof ears (not shown) that extend from the side edges 232 of the absorbentarticle 201 into one of the waist regions. The ears may be integrallyformed with a selected diaper component. For example, the ears may beintegrally formed with the backsheet 217 or from the material employedto provide the top surface, which may include the hollow fibers of thepresent invention, optionally in the form of a nonwoven web. Inalternative configurations, the ears may be provided by membersconnected and assembled to the backsheet 217, the top surface, betweenthe backsheet 217 and top surface, or in various other configurations.As noted above, the ears may contain the hollow fibers of the presentinvention, optionally in the form of a nonwoven web.

As representatively illustrated in FIG. 1, the absorbent article 201 mayalso include a pair of containment flaps 212 that are configured toprovide a barrier and to contain the lateral flow of body exudates. Thecontainment laps 212 may be located along the laterally opposed sideedges 232 of the topsheet 205 adjacent the side edges of the absorbentcore layer 203. The containment flaps 212 may extend longitudinallyalong the entire length of the absorbent core layer 203, or may onlyextend partially along the length of the absorbent core layer 203. Whenthe containment flaps 212 are shorter in length than the absorbent corelayer 203, they may be selectively positioned anywhere along the sideedges 232 of absorbent article 201 in a crotch region 210. In oneembodiment, the containment flaps 212 extend along the entire length ofthe absorbent core layer 203 to better contain the body exudates. Suchcontainment flaps 212 are generally well known to those skilled in theart. For example, suitable constructions and arrangements for thecontainment flaps 212 are described in U.S. Pat. No. 4,704,116 to Enloe.If desired, the containment flaps may contain the hollow fibers of thepresent invention, optionally in the form of a nonwoven web.

The absorbent article 201 may include various elastic or stretchablematerials, such as a pair of leg elastic members 206 affixed to the sideedges 232 to further prevent leakage of body exudates and to support theabsorbent core layer 203. In addition, a pair of waist elastic members208 may be affixed to longitudinally opposed waist edges 215 of theabsorbent article 201. The leg elastic members 206 and the waist elasticmembers 208 are generally adapted to closely fit about the legs andwaist of the wearer in use to maintain a positive, contactingrelationship with the wearer and to effectively reduce or eliminate theleakage of body exudates from the absorbent article 201. The absorbentarticle 201 may also include one or more fasteners 230. For example, twoflexible fasteners 130 are illustrated in FIG. 1 on opposite side edgesof waist regions to create a waist opening and a pair of leg openingsabout the wearer. The shape of the fasteners 230 may generally vary, butmay include, for instance, generally rectangular shapes, square shapes,circular shapes, triangular shapes, oval shapes, linear shapes, and soforth. The fasteners may include, for instance, a hook material, in oneparticular embodiment, each fastener 230 includes a separate piece ofhook material affixed to the inside surface of a flexible backing. Theelastic members (e.g., leg, waist, etc.) and/or fasteners may containthe hollow fibers of the present invention if desired, optionally in theform of a nonwoven web.

The various regions and/or components of the absorbent article 201 maybe assembled together using any known attachment mechanism, such asadhesive, ultrasonic, thermal bonds, etc. Suitable adhesives mayinclude, for instance, hot melt adhesives, pressure-sensitive adhesives,and so forth. When utilized, the adhesive may be applied as a uniformlayer, a patterned layer, a sprayed pattern, or any of separate lines,swirls or dots. In the illustrated embodiment, for example, thebacksheet 217 and topsheet 205 are assembled to each other and to theabsorbent core layer 203 using an adhesive. Alternatively, the absorbentcore layer 203 may be connected to the backsheet 217 using conventionalfasteners, such as buttons, hook and loop type fasteners, adhesive tapefasteners, and so forth. Similarly, other diaper components, such as theleg elastic members 206, waist elastic members 208 and fasteners 230,may also be assembled into the absorbent article 201 using anyattachment mechanism.

Although various configurations of a diaper have been described above,it should be understood that other diaper and absorbent articleconfigurations are also included within the scope of the presentinvention. In addition, the present invention is by no means limited todiapers. In fact, any other absorbent article may be formed inaccordance with the present invention, including, but not limited to,other personal care absorbent articles, such as training pants,absorbent underpants, adult incontinence products, feminine hygieneproducts (e.g., sanitary napkins), swim wear, baby wipes, and so forth;medical absorbent articles, such as garments, fenestration materials,underpads, bandages, absorbent drapes, and medical wipes; food servicewipers; clothing articles; and so forth.

The present invention may be belter understood with reference to thefollowing examples.

Test Methods

Melt Flow Rate:

The melt flow rate (“MFR”) is the weight of a polymer (in grams) forcedthrough an extrusion rheometer orifice (0.0825-inch diameter) whensubjected to a load of 2180 grams in 10 minutes, typically at 190° C.,210° C., or 230° C. Unless otherwise indicated, melt flow rate ismeasured in accordance with ASTM Test Method D1238 with a Tinius OlsenExtrusion Plastometer.

Thermal Properties:

The glass transition temperature (T_(g)) may be determined by dynamicmechanical analysis (DMA) in accordance with ASTM E1640-09. A Q800instrument from TA instruments may be used. The experimental runs may beexecuted in tension/tension geometry, in a temperature sweep mode in therange from −120° C. to 150° C. with a heating rate of 3° C./min. Thestrain amplitude frequency may be kept constant (2 Hz) during the test.Three (3) independent samples may be tested to get an average glasstransition temperature, which is defined by the peak value of the tan δcurve, wherein tan δ is defined as the ratio of the loss modulus to thestorage modulus (tan δ=E″/E′).

The melting temperature may be determined by differential scanningcalonmeiry (DSC). The differential scanning calorimeter may be a DSCQ100 Differential Scanning Calorimeter, which was outfitted with aliquid nitrogen cooling accessory and with a UNIVERSAL ANALYSIS 2000(version 4.6.6) analysis software program, both of which are availablefrom T.A. instruments Inc. of New Castle, Del. To avoid directlyhandling the samples, tweezers or other tools are used. The samples areplaced into an aluminum pan and weighed to an accuracy of 0.01 milligramon an analytical balance. A lid is crimped over the material sample ontothe pan. Typically, the resin pellets are placed directly in theweighing pan.

The differential scanning calorimeter is calibrated using an indiummetal standard and a baseline correction is performed, as described inthe operating manual for the differential scanning calorimeter. Amaterial sample is placed into the test chamber of the differentialscanning calorimeter for testing, and an empty pan is used as areference. All testing is run with a 55-cubic centimeter per minutenitrogen (industrial grade) purge on the test chamber. For resin pelletsamples, the heating and cooling program is a 2-cycle test that beganwith an equilibration of the chamber to −30° C., followed by a firstheating period at a heating rate of 10° C. per minute to a temperatureof 200° C., followed by equilibration of the sample at 200° C. for 3minutes, followed by a first cooling period at a cooling rate of 10° C.per minute to a temperature of −30° C., followed by equilibration of thesample at −30° C. for 3 minutes, and then a second heating period at aheating rate, of 10° C. per minute to a temperature of 200° C. Alltesting is run with a 55-cubic centimeter per minute nitrogen(industrial grade) purge on the test chamber.

The results are evaluated using the UNIVERSAL ANALYSIS 2000 analysissoftware program, which identified and quantified the glass transitiontemperature (T_(g)) of inflection, the endothermic and exothermic peaks,and the areas under the peaks on the DSC plots. The glass transitiontemperature is identified as the region on the plot-line where adistinct change in slope occurred, and the melting temperature isdetermined using an automatic inflection calculation.

Tensile Properties:

The tensile properties may be determined in accordance with ASTM 638-10at 23° C. For instance, individual fiber specimens may initially beshortened (e.g., cut with scissors) to 38 millimeters in length, andplaced separately on a black velvet cloth. 10 to 15 fiber specimens maybe collected in this manner. The fiber specimens may then be mounted ina substantially straight condition on a rectangular paper frame havingexternal dimension of 51 millimeters×51 millimeters and internaldimension of 25 millimeters×25 millimeters. The ends of each fiberspecimen may be operatively attached to the frame by carefully securingthe fiber ends to the sides of the frame with adhesive tape. Each fiberspecimen may be measured for its external, relatively shorter,cross-fiber dimension employing a conventional laboratory microscope,which may be properly calibrated and set at 40× magnification. Thiscross-fiber dimension may be recorded as the diameter of the individualfiber specimen. The frame helps to mount the ends of the sample fiberspecimens in the upper and lower grips of a constant rate of extensiontype tensile tester in a manner that avoids excessive damage to thefiber specimens.

A constant rate of extension type of tensile tester and an appropriateload cell may be employed for the testing. The load cell may be chosen(e.g., 10N) so that the test value falls within 10-90% of the full scaleload. The tensile tester (i.e., MTS SYNERGY 200) and load cell may beobtained torn MTS Systems Corporation of Eden Prairie, Mich. The fiberspecimens in the frame assembly may then be mounted between the grips ofthe tensile tester such that the ends of the fibers may be operativelyheld by the grips of the tensile tester. Then, the sides of the paperframe that extend parallel to the fiber length may be cut or otherwiseseparated so that the tensile tester applies the test force only to thefibers. The fibers may be subjected to a pull test at a pull rate andgrip speed of 12 inches per minute. The resulting data may be analyzedusing a TESTWORKS 4 software program from the MTS Corporation with thefollowing test settings:

Calculation Inputs Test Inputs Break mark drop 50% Break sensitivity 90%Break marker elongation 0.1 in Break threshold 10 g_(f) Nominal gagelength 1 in Date Acq. Rate 10 Hz Slack pre-load 1 lb_(f) Denier length9000 m Slope segment length 20% Density 1.25 g/cm³ Yield offset 0.20%  Initial speed 12 in/min Yield segment length  2% Secondary speed 2in/min

The tenacity values may be expressed in terms of gram-force per denier.Peak elongation (% strain at break) and peak stress may also bemeasured.

The peak load of a web may be determined using a 2″×6″ strip cut alongthe length (MD) and width direction (CD). The test may be performed in auniversal tensile tester equipped with two 1″×3″ rubber coated grips.The gauge length may be 76±1 mm (3±0.04″).

Density and Percent Void Volume:

To determine density and percent void volume, the width (W_(i)) andthickness (T_(i)) of the specimen may be initially measured prior todrawing. The length (L_(i)) before drawing may also be determined bymeasuring the distance between two markings on a surface of thespecimen. Thereafter, the specimen may be drawn to initiate poreformation. The width (W_(f)), thickness (T_(f)), and length (L_(f)) ofthe specimen may then be measured to the nearest 0.01 mm utilizingDigimatic Caliper (Mitutoyo Corporation). The volume (V_(i)) beforedrawing may be calculated by W_(i)×T_(i)×L_(i)=V_(i). The volume (V_(f))after drawing may also be calculated by W_(f)×T_(f)×L_(f)=V_(f). Thedensity (P_(f)) may be calculated by P_(f)=P_(i)/ϕ, where P_(i) isdensity of precursor material, and the pement void volume (% V_(v)) wascalculated by: % V_(v)=(1−1/ϕ)×100.

Hydrostatic Presure Test (“Hydrohead”):

The hydrostatic pressure test is a measure of the resistance of amaterial to penetration by liquid water under a static pressure and isperformed in accordance with AATCC Test Method 127-2008. The results foreach specimen may be averaged and recorded in centimeters (cm). A highervalue indicates greater resistance to water penetration.

Water Vapor Transmission Rate (“WVTR”):

The test used to determine the WVTR of a material may vary based on thenature of the material. One technique for measuring the WVTR value isASTM E96/96M-12, Procedure B. Another method involves the use of INDATest Procedure IST-70.4 (01). The INDA test procedure is summarized asfollows. A dry chamber is separated from a wet chamber of knowntemperature and humidity by a permanent guard film and the samplematerial to be tested. The purpose of the guard film is to define adefinite air gap and to quiet or still the air in the air gap while theair gap is charactehzed. The dry chamber, guard film, and the wetchamber make up a diffusion cell in which the test film is sealed. Thesample holder is known as the Permatran-W Model 100K manufactured byMocon/Modem Controls, Inc., Minneapolis, Minn. A first test is made ofthe WVTR of the guard film and the air gap between an evaporatorassembly that generates 100% relative humidity. Water vapor diffusesthrough the air gap and the guard film and then mixes with a dry gasflow that is proportional to water vapor concentration. The electricalsignal is routed to a computer for processing. The computer calculatesthe transmission rate of the air gap and the guard film and stores thevalue for further use.

The transmission rate of the guard film and air gap is stored in thecomputer as CalC. The sample material is then sealed in the test cell.Again, water vapor diffuses through the air gap to the guard film andthe test material and then mixes with a dry gas flow that sweeps thetest material. Also, again, this mixture is carried to the vapor sensor.The computer then calculates the transmission rate of the combination ofthe air gap, the guard film, and the test material. This information isthen used to calculate the transmission rate at which moisture istransmitted through the test material according to the equation:TR ⁻ _(1test material) =TR ⁻ _(1test material,guardfilm,airgap) −TR ⁻¹_(guardfilm,airgap)

The water vapor transmission rate (“WVTR”) is then calculated asfollows:

${WVTR} = \frac{F\;\rho_{{sat}{(T)}}{RH}}{{AP}_{{sat}{(T)}}\left( {1 - {RH}} \right)}$wherein,

-   -   F=the flow of water vapor in cm³ per minute;    -   ρ_(sat(T))=the density of water in saturated air at temperature        T;    -   RH=the relative humidity at specified locations in the cell;    -   A=the cross sectional area of the cell; and    -   P_(sat(T))=the saturation vapor pressure of water vapor at        temperature T.        Frazer Porosity:

The Frazier porosity was measured in a Frazier® Low DifferentialPressure Air Permeability Tester (FAP-LP) by citing an 8″ strip(measured along the machine direction) of a sample and folding thesample accordion style (in the cross direction) to obtain six layers.

EXAMPLE 1

A precursor polymer blend was made that contained 91.8 wt % of isotacticpolypropylene (M3661, melt flow rate of 14 g/10 min at 230° C. andmelting temperature of 150*° C., Total Petrochemicals), 7.45% polylacticacid (PLA) (Ingeo 6251D, melt flow rate 70-85 g/10 at 210° C.,Natureworks), and 0.75% polyepoxide compatibilizer (Arkema Lotader®AX8900). The polyepoxide modifier was poly(ethylene-co-methylacrylate-co-glycidyl methacrylate) (Lotader® AX8900, Arkema) having amelt flow rate of 5-6 g/10 min (190° C./2160 g), a glycidyl methacrylatecontent of 7 to 11 wt. %, methyl acrylate content of 13 to 17 wt. %, andethylene content of 72 to 80 wt. %. The components were compounded in aco-rotating twin screw extruder (Werner and Pfleiderer ZSK-30 with adiameter of 30 mm and a L/D=44). The extruder had seven heating zones.The temperature in the extruder ranged from 180° C. to 220° C. Thepolymer was fed gravimetricaly to the extruder at the hoper at 6.8Kilograms per hour (15 pounds per hour). The extruder was operated at200 revolutions per minute (RPM). In the last section of the barrel(front), a 3-hole die of 6 mm in diameter was used to form theextrudate. The extrudate was air-cooled in a conveyor belt andpelletized using a Conair Pelletizer.

Hollow monocomponent fibers were produced in a fiber line equipped with2 single screw extruders (1.25-in diameter). The extruders fed thepolymer composition into a spinneret containing 288 capillaries of4C-segments capillary design. The fibers were spun at a rate of 0.5grams per minute per hole at a spinning velocity of 118 meters perminute and collected in spools for post-stretching process. Theextrusion temperature profile was as follows: Zone 1=210° C., Zone2=220° C., Zone 3=220° C., Zone 4=220° C., and Spin Beam=220° C. Thefiber was air quenched at a temperature of 18.3° C. Before drawing, thefibers had an average diameter of 80 micrometers with a hollow area ofappropriately 25% of the total cross-sectional area. The quenched fiberswere wound in spools for the post cold drawing process. The fibers werecold drawn to 400% using a hydraulic frame at a speed of 4000millimeters per minutes. The fibers were then cut with a razor blade inliquid nitrogen and analyzed via scanning electron microscopy. Thefractured surfaced were sputter-coated with gold-palladium in a DentonVacuum Desk V sputtering system using 15 mA for 75 s and analyzed viaSEM in a Field Emission Quanta 650. The results are set forth in FIGS.5-6. The hollow area was estimated to be 25%.

EXAMPLE 2

Hollow bicomponent fibers were produced in a bicomponent fiber lineequipped with 2 single screw extruders (1.25-in diameter). Thebicomponent fiber had a 50/50, sheath/core configuration, in which thesheath was formed from 100 wt. % polypropylene (Achieve 3854) and thecore was formed from the blend described in Example 1. The extruders fedthe sheath and core polymer compositions into a spinneret containing 72capillaries of 4C-segments capillary design. The fibers were spun at arate of 0.45 grams per minute per hole at a spinning velocity of 200meters per minute and collected in spools for post-stretching process.The extrusion temperature profile for both sheath and core was asfollows: Zone 1=220° C., Zone 2=225° C., Zone 3=230° C., Zone 4=240° C.,and Spin Beam=240° C. The fiber was quenched in a water bath located 35cm below the spinneret. The quenched fibers were then stretched at roomtemperature (25° C.) to 300% between two godet rolls (single step draw).The feed roll was operated at 50 meter per minute and the take up rollat roll at 200 meters per minute. The fibers were then cut with a razorblade in liquid nitrogen and analyzed via scanning electron microscopy.The fractured surfaced were sputter-coated with gold-palladium in aDenton Vacuum Desk V sputtering system using 15 mA for 75 s and analyzedvia SEM in a Field Emission Quanta 650. The results are set forth inFIGS. 7-8. Various properties of the fibers were also tested as providedin the table below.

Dimeter (μm) 31.4 Tenacity (g/den) 3.8 Peak Stress (MPa) 303.8 Strain atBreak (%) 90.0 Energy per volume at break (J/cm³) 223.1

While the invention has been described in detail with respect to thespecific embodiments thereof, it will be appreciated that those skilledin the art, upon attaining an understanding of the foregoing, mayreadily conceive of alterations to, variations of, and equivalents tothese embodiments. Accordingly, the scope of the present inventionshould be assessed as that of the appended claims and any equivalentsthereto.

What is claimed is:
 1. A drawn hollow fiber that generally extends in alongitudinal direction, the hollow fiber comprising a hollow cavity thatextends along at least a portion of the fiber in the longitudinaldirection, wherein the cavity is defined by an interior wall that isformed from a thermoplastic composition containing a continuous phasethat includes a polyolefin matrix polymer and a polymeric nanoinclusionadditive dispersed within the continuous phase in the form of discretedomains, wherein the polymeric nanoinclusion additive constitutes from0.05 wt. % to 20 wt. % of the thermoplastic composition based on theweight of the polyolefin matrix polymer, wherein a porous network isdefined in the thermoplastic composition that includes a plurality ofnanopores, and wherein the hollow fiber has an average inner diameter offrom 1 to less than 100 micrometers and an average outer diameter offrom 2 to 100 micrometers wherein the inner diameter is smaller than theouter diameter.
 2. The drawn hollow fiber of claim 1, wherein theinterior wall has an average wall thickness of from 0.5 to 50micrometers.
 3. The drawn hollow fiber of claim 1, wherein the interiorwall has an inner diameter greater than the thickness of the interiorwall.
 4. The drawn hollow fiber of claim 3, wherein the average innerdiameter of the interior wall is from 1 to 60 micrometers.
 5. The drawnhollow fiber of claim 1, wherein the interior wall has an average outerdiameter of from 2 to 50 micrometers.
 6. The drawn hollow fiber of claim1, wherein the nanopores have an average cross-sectional dimension of800 nanometers or less.
 7. The drawn hollow fiber of claim 1, whereinthe polyolefin matrix polymer has a melt flow rate of from 0.5 to 80grams per 10 minutes as determined at a load of 2160 grams and at 230°C. in accordance with ASTM D1238.
 8. The drawn hollow fiber of claim 1,wherein the polyolefin matrix polymer is a isotactic polypropylenehomopolymer or a copolymer containing at least 90% by weight propylene.9. The drawn hollow fiber of claim 1, wherein the continuous phaseconstitutes from 60 wt. % to 99 wt. % of the thermoplastic composition.10. The drawn hollow fiber of claim 1, wherein the polymericnanoinclusion additive is a polyepoxide.
 11. The drawn hollow fiber ofclaim 1, wherein the polymeric nanoinclusion additive has a melt flowrate of from 0.1 to 100 grams per 10 minutes as determined at a load of2160 grams and at a temperature at least 40° C. above the meltingtemperature in accordance with ASTM D1238.
 12. The drawn hollow fiber ofclaim 1, wherein the thermoplastic composition further comprises amicroinclusion additive dispersed within the continuous phase in theform of discrete domains.
 13. The drawn hollow fiber of claim 12,wherein the polymer of the microinclusion additive is polylactic acid.14. The drawn hollow fiber of claim 12, wherein the polymer of themicroinclusion additive has a glass transition temperature of 0° C. ormore.
 15. The drawn hollow fiber of claim 1, wherein the thermoplasticcomposition further comprises an interphase modifier.
 16. The drawnhollow fiber of claim 1, wherein the porous network further includesmicropores.
 17. The drawn hollow fiber of claim 1, wherein the fiber isa bicomponent fiber having a sheath surrounding a core that togetherform the interior wall of the hollow fiber, wherein the core is formedfrom the thermoplastic composition.
 18. The hollow fiber of claim 1,wherein the hollow fiber has an average inner diameter of from 1 to 100micrometers and an average outer diameter of from 2 to 100 micrometers.19. A nonwoven web comprising the drawn hollow fiber of claim
 1. 20. Anabsorbent article comprising the nonwoven web of claim 19, wherein theabsorbent article includes a liquid-impermeable layer, liquid-permeablelayer, and an absorbent core, wherein the liquid-impermeable layer, theliquid-permeable layer, or both include the nonwoven web.
 21. A methodfor forming a hollow fiber, the method comprising: forming athermoplastic composition that contains a continuous phase that includesa polyolefin matrix polymer and a polymeric nanoinclusion additivedispersed within the continuous phase in the form of discrete domains;extruding the thermoplastic composition through a capillary to form thefiber, wherein one or more shaped slots are positioned within thecapillary; and drawing the fiber at a temperature that is lower than themelting temperature of the matrix polymer, thereby forming a porousnetwork that includes a plurality of nanopores, wherein the hollow fiberhas an average inner diameter of from 1 to 100 micrometers and anaverage outer diameter of from 2 to 100 micrometers.
 22. The method ofclaim 21, wherein the thermoplastic composition is stretched to a drawratio of from 1.1 to
 25. 23. The method of claim 21, wherein the fiberis drawn at a temperature from −50° C. to 150° C.